Vapor deposition apparatus and techniques using high purity polymer derived silicon carbide

ABSTRACT

Organosilicon chemistry, polymer derived ceramic materials, and methods. Such materials and methods for making polysilocarb (SiOC) and Silicon Carbide (SiC) materials having 3-nines, 4-nines, 6-nines and greater purity. Vapor deposition processes and articles formed by those processes utilizing such high purity SiOC and SiC.

This application is a continuation of U.S. patent application Ser. No.15/275,055, filed Sep. 23, 2016, which: (i) claims under 35 U.S.C. §119(e)(1) the benefit U.S. provisional application Ser. No. 62/232,355filing date of Sep. 24, 2015; and (ii) is a continuation-in-part of U.S.patent application Ser. No. 14/864,125 filed Sep. 24, 2015, which claimsunder 35 U.S.C. § 119(e)(1) the benefit of US provisional applicationSer. No. 62/055,461 filing date of Sep. 25, 2014 and U.S. provisionalapplication Ser. No. 62/055,497 filing date of Sep. 25, 2014, the entiredisclosures of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present inventions relate to improvements in vapor depositionprocesses and crystal growth and materials growth that can be achievedusing the novel ultra pure SiC and SiOC materials that are disclosed andtaught in patent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344), filedcontemporaneously herewith, the entire disclosures of each of which areincorporated herein by reference.

The use of these materials having 6-nines, 7-nines, 8-nines and greaterpurity provides from many advantages in vapor deposition growth ofcrystals. And provides for new and refined vapor deposition apparatusand systems for crystal growth. The ultra high purity materials provide,among other things: faster crystal growth, the ability to grow largerand purer seed crystals or starting plates for the deposition process;the ability to use a larger percentage of the starting material used inthe apparatus. Thus, enhanced control, greater efficiencies and highquality can be obtained by using the high purity and ultra purematerials in vapor deposition techniques.

In recent years the demand for high purity silicon carbide, and inparticular high purity single crystalline carbide materials for use inend products, such as a semiconductor, has been increasing, but isbelieve to be unmet. For example, “single crystals are gaining more andmore importance as substrate[s] for high frequency and high powersilicon carbide electronic devices.” Wang, et.al, Synthesis of HighPower Sic Powder for High-resistivity SiC Single crystals Growth, p. 118(J. Mater. Sic. Technol. Vol. 23, No 1, 2007)(hereinafter Wang). Toobtain these high purity silicon carbide end products, silicon carbidepowder as a starting or raw material must be exceedingly pure. However,“[c]ommercially available SiC powder is usually synthesized bycarbothermal reduction of silica. Unfortunately, it is typicallycontaminated to the level that makes it unsuitable for SiC growth.”Wang, at p. 118.

The longstanding need for, and problem of obtaining high purity siliconcarbide, and the failing of the art to provide a viable (both from atechnical and economical standpoint) method of obtaining this materialwas also recognized in Zwieback et al., 2013/0309496 (“Zwieback”), whichprovides that the “[a]vailability of high-purity SiC source material isimportant for the growth of SiC single crystals in general, and it iscritical for semi-insulating SiC crystals” (Zwieback at ¶0007). Zwiebackgoes on to state that the prior methods including liquid based methodshave consistently failed to meet this need: “While numerousmodifications of the Acheson process have been developed over the years,the produced SiC material always contain high concentrations of boron,nitrogen aluminum and other metals, and is unsuitable as a sourcematerial for the growth of semiconductor-quality SiC crystals” (Zwiebackat ¶0009); “commercial grade bulk SiC produced by CVD is not pure enoughfor the use as a source in SiC crystal growth” (Zwieback at ¶0010); theliquid process “produced SiC material contains large concentrations ofcontaminates and is unsuitable for the growth of semiconductor-qualitySiC crystals” (Zwieback at ¶0011); and, the direct synthesis of SiCprovides an impure material that “precludes the use of such material”(Zwieback at ¶0015). Zwieback itself seeks to address this long-standingneed with a complex, multi-step version of what appears to be the directprocess in a stated attempt to provide high purity SiC. It is believedthat this process is neither technically or economically viable; andtherefor that it cannot solve the longstanding need to providecommercial levels of high purity SiC.

Thus, although there are other known methods of obtaining siliconcarbide, it is believed that none of these methods provide the requisitetechnical, capacity, and economical viability to provide the puritylevels, amounts, and low cost required for commercial utilization andapplications; and in particular to meet the ever increasing demands forsemiconductor grade material, and other developing commercialutilizations and applications. “Among these synthesis methods, only CVDhas been successfully used to produce high purity SiC powder, it is notsuitable for mass production because of high costs associated with CVDtechnology.” Wang, at p. 118.

CVD generally refers to Chemical Vapor Deposition. CVD is a type ofvapor deposition technology. In addition to CVD, vapor depositiontechnologies would include PVD (Physcial Vapor Deposition), plasmaenhanced CVD, Physical Vapor Transport (PVT) and others.

Thus, for these end products, and uses, among others that require highpurity materials, there is an ever increasing need for low cost siliconcarbide raw material that has a purity of at least about 99.9%, at leastabout 99.99%, at least about 99.999%, and least about 99.9999% and atleast about 99.99999% or greater. However, it is believe that prior toembodiments disclosed and taught in patent applications, Ser. No.14/864,539 (US Publication No. 2016/0208412), Ser. No. 14/864,125 (USPublication No. 2016/0207782), and PCT/US2015/051997 (Publication No. WO2016/049344), for all practical purposes, this need has gone unmet.

Further, prior to embodiments of the inventions disclosed and taught inSer. No. 14/864,539 (US Publication No. 2016/0208412), Ser. No.14/864,125 (US Publication No. 2016/0207782), and PCT/US2015/051997(Publication No. WO 2016/049344), it is believed that high purity andultrahigh purity SiOC materials, and in particular in quantities largerthan small laboratory batches of a few ounces, have never been obtained,and thus their importance, benefits, and the need for such material, hasgone largely unrecognized and unappreciated.

High purity single crystalline silicon carbide material has manydesirable features and characteristics. For example, it is very hardhaving a Young's modulus of about 424 GPa. Polycrystalline siliconcarbide may also have very high hardness, depending upon its grainstructure and other factors.

As used herein, unless specified otherwise, the terms specific gravity,which is also called apparent density, should given their broadestpossible meanings, and generally mean weight per until volume of astructure, e.g., volumetric shape of material. This property wouldinclude internal porosity of a particle as part of its volume. It can bemeasured with a low viscosity fluid that wets the particle surface,among other techniques.

As used herein, unless specified otherwise, the terms actual density,which may also be called true density, should be given their broadestpossible meanings, and general mean weight per unit volume of amaterial, when there are no voids present in that material. Thismeasurement and property essentially eliminates any internal porosityfrom the material, e.g., it does not include any voids in the material.

Thus, a collection of porous foam balls (e.g., Nerf® balls) can be usedto illustrate the relationship between the three density properties. Theweight of the balls filling a container would be the bulk density forthe balls:

${{Bulk}{Density}} = \frac{{weight}{of}{balls}}{{volume}{of}{container}{filled}}$

The weight of a single ball per the ball's spherical volume would be itsapparent density:

${{Apparent}{Density}} = \frac{{weight}{of}{one}{ball}}{{volume}{of}{that}{ball}}$

The weight of the material making up the skeleton of the ball, i.e., theball with all void volume removed, per the remaining volume of thatmaterial would be the actual density:

${Actual}{Density}{= \frac{{weight}{of}{material}}{{volume}{of}{void}{free}{material}}}$

As used herein, unless stated otherwise, room temperature is 25° C. And,standard ambient temperature and pressure is 25° C. and 1 atmosphere.

Generally, the term “about” as used herein unless specified otherwise ismeant to encompass a variance or range of ±10%, the experimental orinstrument error associated with obtaining the stated value, andpreferably the larger of these.

SUMMARY

There has been a long-standing and unfulfilled need for, among otherthings, improved and enhanced methods of vapor deposition SiC crystalgrowth.

The present inventions, among other things, solve these needs byproviding the compositions, materials, articles of manufacture, devicesand processes taught, disclosed and claimed herein.

Still additionally there are provided compositions, methods and articleshaving one or more of the following features: wherein the volumetricshape of silicon carbide has less than about 50 ppm total of theelements selected from the group consisting of Al, Fe, B, and P; whereinthe volumetric shape of silicon carbide has less than about 40 ppm totalof the elements selected from the group consisting of Al, Fe, B, and P;wherein the volumetric shape of silicon carbide has less than about 100ppm total of the elements selected from the group consisting of Al, Fe,B and P wherein the volumetric shape of silicon carbide has less thanabout 1000 ppm total of the elements selected from the group consistingof Al, Fe, B and P; wherein the volumetric shape of silicon carbide hasless than about 50 ppm total of the elements selected from the groupconsisting of Ti, Al, Fe, B, P, Pt, Ca, Mg, Li and Na; wherein thevolumetric shape of silicon carbide has less than about 50 ppm total ofthe elements selected from the group consisting of Al, Fe, B, P, Pt, Ca,Mg, Li, Na, Ni, V, Pr, Ce, Cr, S and As; wherein the volumetric shape ofsilicon carbide has less than about 50 ppm total of the elementsselected from the group consisting of Al, Fe, B, P, Pt, Ca, Mg, Li, Na,Ni, V, Ti, Ce, Cr, S and As; and, wherein the volumetric shape ofsilicon carbide has less than about 50 ppm total of the elementsselected from the group consisting of Al, Fe, B, P, Pt, Ca, Mg, Li, Na,Ni, V, Pr, Ce, Cr, S and As.

Still additionally there are provided compositions, methods and articleshaving one or more of the following features: wherein the siliconcarbide has less than about 90 ppm total of the elements selected fromthe group consisting of Ti, Al, Fe, B, P, Pt, Ca, Ce, Cr, S and As;wherein the silicon carbide has less than about 90 ppm total of theelements selected from the group consisting of Ti, Fe, P, Pt, Ca, Mg,Li, Na, Ni, Cr and As; wherein the silicon carbide has less than about90 ppm total of the elements selected from the group consisting of Al,Fe, B, P, Mg, Li, V, Ce, Cr, and S; wherein the silicon carbide has lessthan about 90 ppm total of the elements selected from the groupconsisting of Al, Fe, B, and P; wherein the silicon carbide has lessthan about 90 ppm total of the elements selected from the groupconsisting of Ti, Al, Fe, B, P, Pt, Ca, Ce, Cr, S and As; wherein thesilicon carbide has less than about 90 ppm total of the elementsselected from the group consisting of Ti, Fe, P, Pt, Ca, Mg, Li, Na, Ni,Cr and As; wherein the silicon carbide has less than about 90 ppm totalof the elements selected from the group consisting of Al, Fe, B, P, Mg,Li, V, Ce, Cr, and S; and, wherein silicon carbide is produced andwherein the silicon carbide is at least 99.9999% pure; and the siliconcarbide is beta type.

Accordingly there is provided a a high purity polymer derived ceramicSiC composition, the composition including: an SiC₄ configuration; thecomposition defining a surface, wherein the composition surface isresistant to oxidation under standard ambient temperature and pressure,whereby the surface is essentially free of an oxide layer at standardambient temperature and pressure; and, wherein the composition issubstantially free from impurities, whereby total impurities are lessthan 1 ppm.

There is provided methods, composition and articles having one or moreof the following features: wherein the SiC₄ configuration is selectedfrom the group consisting of cube structures and tetrahedral structures;wherein the SiC₄ configuration is selected from the group consisting ofhexagonal, rhombohedral, and trigonal structures; wherein the SiC₄configuration is selected from the group consisting of 3C—SiC, β-SiC,2H—SiC, 4H—SiC, 6H—SiC, 8H, 10H, 16H, 18H, 19H, 15R, 21R, 24H, 33R, 39R,27R, 48H, and 51R; wherein the SiC₄ configuration is selected from thegroup consisting of a stacking sequence of ABCABC, a stacking sequenceof ABAB, a stacking sequence of ABCBABCB, and a stacking sequence ofABCACBABCACB.

Still further there is provided a semiconductor including an SiC wafermade from the high purity polymer derived ceramic SiC composition havinga band gap, wherein the band gap is from about 2.26 eV to about 3.33 eV.

Additionally there is provided a semiconductor including an SiC wafermade from the high purity polymer derived ceramic SiC composition havinga band gap, wherein the band gap is greater than about 2.20 eV.

Further there is provided a semiconductor including an SiC wafer madefrom the high purity polymer derived ceramic SiC composition having aband gap, wherein the band gap is from about 2.26 eV to about 3.33 eV.

Yet further there is provided a power device including an SiC wafer madefrom the high purity polymer derived ceramic SiC composition having anE_(max), wherein the E_(max) is greater than about 1 MV/cm.

Additionally there is provided a power device including an SiC wafermade from the high purity polymer derived ceramic SiC composition havingan E_(max), wherein the E_(max) is greater than about 1.5 MV/cm.

Yet further there is provided a power device including an SiC wafer madefrom the high purity polymer derived ceramic SiC composition having anE_(max), wherein the E_(max) is greater than about 2 MV/cm.

Furthermore, there is provided a power device including an SiC wafermade from the high purity polymer derived ceramic SiC composition havingan E_(max), wherein the E_(max) is greater than about 2.5 MV/cm.

Moreover, there is provided a high frequency device including an SiCwafer made from the high purity polymer derived ceramic SiC compositionhaving a saturation drift velocity of 2×10⁷ cm/sec².

Still further there is provided an article made from the high puritypolymer derived ceramic SiC composition having a thermal conductivity,the thermal conductivity being greater than about 4.0 W/(cm-K) at roomtemperature.

Still additionally there is provided an article made from the highpurity polymer derived ceramic SiC composition having a thermalconductivity, the thermal conductivity being greater than about 4.5W/(cm-K) at room temperature.

Still additionally there are provided methods, compositions and articleshaving one or more of the following features: wherein the volumetricshape defines a surface, wherein the surface is essentially free of anoxide layer; wherein the volumetric shape is selected from the group ofshapes consisting of pucks, briquettes, bricks, pellets, discs, pillsand tablets; wherein the volumetric shape is selected from the group ofshapes consisting of pucks, briquettes, bricks, pellets, discs, pillsand tablets; wherein the volumetric shape elastic modules is less thanabout 100 GPa, and a compressive strength of less than about 1,000 MPa;wherein the volumetric shape elastic modules is less than about 100 GPa,and a compressive strength of less than about 1,000 MPa; wherein thevolumetric shape elastic modules is less than about 10 GPa, and acompressive strength of less than about 500 MPa; wherein the volumetricshape elastic modules is less than about 10 GPa, and a compressivestrength of less than about 500 MPa; a friable mass wherein theimpurities are less than about 1 ppm; a friable mass wherein the SiC₄configuration is selected from the group consisting of cube structuresand tetrahedral structures; a friable mass wherein the SiC₄configuration is selected from the group consisting of hexagonal,rhombohedral, and trigonal structures; a friable mass wherein the SiC₄configuration is selected from the group consisting of 3C—SiC, β-SiC,2H—SiC, 4H—SiC, 6H—SiC, 8H, 10H, 16H, 18H, 19H, 15R, 21R, 24H, 33R, 39R,27R, 48H, and 51R; a friable mass wherein the SiC₄ configuration isselected from the group consisting of a stacking sequence of ABCABC, astacking sequence of ABAB, a stacking sequence of ABCBABCB, and astacking sequence of ABCACBABCACB; and a friable mass wherein the SiC₄configuration is selected from the group consisting of a stackingsequence of ABCABC, a stacking sequence of ABAB, and a stacking sequenceof ABCBABCB.

Yet further the is provided an epitaxial polysilocarb derived SiC layeron a substrate, wherein the epitaxial polysilocarb derived SiC layer ismade from: a high purity polymer derived ceramic SiC compositionincluding: an SiC₄ configuration; the composition defining a surface,wherein the composition surface is resistant to oxidation under standardambient temperature and pressure, whereby the surface is essentiallyfree of an oxide layer at standard ambient temperature and pressure;and, wherein the composition is substantially free from impurities,whereby total impurities are less than 1 ppm; whereby the epitaxialpolysilocarb derived SiC layer is substantially free from impuritieshaving less than 1 ppm impurities.

There is yet further provided methods, compositions and articles havingone or more of the following features: wherein the impurities areselected from the group consisting of Al, Fe, B, P, Pt, Ca, Mg, Li, Na,Ni, V, Ti, Ce, Cr, S and As; wherein the impurities are selected fromthe group consisting of Al, Fe, B, P, Pt, Ca, Mg, Li, Na, Ni, V, Ti, Ce,Cr, S and As; wherein the impurities are selected from the groupconsisting of Al, Fe, B, P and N; wherein the impurities are selectedfrom the group consisting of Al, Fe, B, P and Na; wherein the impuritiesare selected from the group consisting of Al, Fe, B, P and Na; whereinthe impurities are selected from the group consisting of Al, B, and P;wherein the substrate is comprised of SiC; and wherein the substrate iscomprised of Si; wherein the substrate is comprised of a tie layer andSiOC.

Still further there is provided an epitaxial polysilocarb derived SiClayer on a substrate, wherein the epitaxial polysilocarb derived SiClayer is made from: a friable mass of high purity polymer derivedceramic SiC, including: polymer derived SiC granular particles, theparticles including an SiC₄ configuration; the granular particlesdefining a volumetric shape; the granular particles having an actualdensity of about 3.0 g/cc to about 3.5 g/cc, an elastic modules of about410 GPa, and a compressive strength of about 3,900 MPa; the volumetricshape having an apparent density of less than about 2.5 g/cc, an elasticmodules of less than about 205 GPa, and a compressive strength of lessthan about 2,000 MPa; and, wherein the volumetric shape is substantiallyfree from impurities, whereby total impurities, the impurities selectedfrom the group consisting of Al, Fe, and B, are less than 10 ppm,

Yet further there is provided a polysilocarb derived SiC boule,including: the polysilocarb derived SiC boule defining a length and adiameter, wherein the length is greater than about 1 inch and thediameter is greater than about 2 inches; wherein the polysilocarbderived SiC boule is made by the vapor deposition of a high puritypolymer derived ceramic SiC composition including: an SiC₄configuration; the composition defining a surface, wherein thecomposition surface is resistant to oxidation under standard ambienttemperature and pressure, whereby the surface is essentially free of anoxide layer at standard ambient temperature and pressure; and, whereinthe composition is substantially free from impurities, whereby totalimpurities are less than 1 ppm; whereby the polysilocarb derived SiCboule is substantially free from impurities having less than 1 ppmimpurities, and is essentially free from micropipes.

Additionally there is provided methods, compositions and articles havingone or more of the following features: a polysilocarb derived SiC boulewherein length is at least 3 inches; a polysilocarb derived SiC boulewherein length is at least 5 inches; a polysilocarb derived SiC boulewherein length is at least 8 inches; a polysilocarb derived SiC boulewherein length is at least 12 inches; a polysilocarb derived SiC boulewherein the diameter is at least 4 inches; a polysilocarb derived SiCboule wherein the diameter is at least 8 inches; a polysilocarb derivedSiC boule wherein the diameter is at least 10 inches; a polysilocarbderived SiC boule wherein the diameter is at least 12 inches; apolysilocarb derived SiC boule wherein the diameter is at least 9 inchesand the length is at least 4 inches; a polysilocarb derived SiC boulewherein the diameter is at least 10 inches and the length is at least 4inches; a polysilocarb derived SiC boule wherein the diameter is atleast 12 inches and the length is at least 4 inches; and, a polysilocarbderived SiC boule wherein the diameter is at least 11 inches and thelength is at least 4 inches.

Still further there is provided a polysilocarb derived SiC boule,including: the polysilocarb derived SiC boule defining a length and adiameter, wherein the length is greater than about 1 inch and thediameter is greater than about 2 inches; wherein the polysilocarbderived SiC boule is made by the vapor deposition of a friable mass ofhigh purity polymer derived ceramic SiC, the friable mass including:polymer derived SiC granular particles, the particles including an SiC₄configuration; the granular particles defining a volumetric shape; thegranular particles having an actual density of about 3.0 g/cc to about3.5 g/cc, an elastic modules of about 410 GPa, and a compressivestrength of about 3,900 MPa; and, the volumetric shape having anapparent density of less than about 2.0 g/cc, an elastic modules of lessthan about 100 GPa, and a compressive strength of less than about 1,000MPa; wherein the volumetric shape is substantially free from impurities,whereby total impurities, the impurities selected from the groupconsisting of Al, Fe, B, P, Ca, Mg, Na, Ni, Cr, S and As, are less than10 ppm; and, whereby the polysilocarb derived SiC boule is substantiallyfree from micropipes.

There is still further provided polysilocarb derived SiC boules: whereinthe boule has less than 5 micropipes/cm²; wherein the boule has lessthan 1 micropipes/cm²; wherein the boule has less than 0.5micropipes/cm²; and wherein the boule has less than 0.1 micropipes/cm².

Additionally there is provided a method of making a polysilocarb derivedSiC boule, the polysilocarb derived SiC boule defining a length and adiameter, wherein the length is greater than about 1 inch and thediameter is greater than about 2 inches, the method including: whereinthe polysilocarb derived SiC boule is made by the vapor deposition of amass of high purity polymer derived ceramic SiC, the mass including:polymer derived SiC granular particles, the particles including an SiC₄configuration; the granular particles defining a volumetric shape; thegranular particles having an actual density of about 3.0 g/cc to about3.5 g/cc, an elastic modules of about 410 Gpa, and a compressivestrength of about 3,900 MPa; and, the volumetric shape having a bulkdensity of less than about 2.0 g/cc, an elastic modules of less thanabout 100 Gpa, and a compressive strength of less than about 1,000 MPa;wherein the volumetric shape is substantially free from impurities,whereby total impurities, the impurities selected from the groupconsisting of Al, Fe, and B, are less than 10 ppm; and, whereby thepolysilocarb derived SiC boule has less than 1 micropipe/cm².

Moreover, there is provided a method of making a polysilocarb derivedSiC boule, the polysilocarb derived SiC boule defining a length and adiameter, wherein the length is greater than about 1 inch and thediameter is greater than about 2 inches, the method including: whereinthe polysilocarb derived SiC boule is made by the vapor deposition of afriable mass of high purity polymer derived ceramic SiC, the friablemass including: polymer derived SiC granular particles, the particlesincluding an SiC₄ configuration; the granular particles defining avolumetric shape; the granular particles having an actual density ofabout 3.0 g/cc to about 3.5 g/cc, an elastic modules of about 410 GPa,and a compressive strength of about 3,900 MPa; and, the volumetric shapehaving an apparent density of less than about 2.0 g/cc, an elasticmodules of less than about 100 GPa, and a compressive strength of lessthan about 1,000 MPa; wherein the volumetric shape is substantially freefrom impurities, whereby total impurities, the impurities selected fromthe group consisting of Al, Fe, B, P, Ca, Mg, Na, Ni, Cr, S and As, areless than 10 ppm; and, whereby the polysilocarb derived SiC boule issubstantially free from micropipes.

Thus, there is provided a method of making a high purity siliconoxycarbide, the method including: distilling a liquid including silicon,carbon and oxygen; and, curing the liquid to a cured material; whereincured material is at least 99.999% pure.

Thus, there is provide a method of making boule for the production of asilicon carbide wafer characterized with the properties of 2″ 6H N-Type,6H—N 2″ dia, type/dopant:N/nitrogen orientation:<0001>+/−0.5 degree,thickness:330±25 um D Grade,MPDä100 cm-2, D Grade,RT:0.02-0.2 Ω·cm, themethod including the steps of forming a vapor of a polymer derivedceramic SiC, the polymer derived ceramic having a purity of at leastabout 6 nines, and being oxide layer free, depositing the vapor on aseed crystal to form a boule, and providing the boule to a wafermanufacturing process.

Moreover, there are provided the methods, boules and wafer having one ormore of the following features: wherein the seed comprises a polymerderived ceramic SiC; wherein the wafer making process produces a waferhaving improved features, when compared to a wafer made from anon-polymer derived SiC material; and wherein the improved features areselected from the group consisting of bow, edge contour, flatness, focalplane, warp and site flatness.

Still further there is provided a method of making silicon carbidewafer, the method comprising the steps of forming a vapor of a polymerderived ceramic SiC, the polymer derived ceramic having a purity of atleast about 6 nines, and being oxide layer free, depositing the vapor ona seed crystal to form a boule, and providing the boule to a wafermanufacturing process.

Additionally, there is provided a method of making a wafer from polymerderived ceramic starting materials wherein the wafer is characterizedwith the properties of 2″ to 10″ 6H N-Type.

Yet further there is provided a method of making boule for theproduction of a silicon carbide wafer characterized with the propertiesof 4H—N 2″ to 10″ dia, type/dopant:N/nitrogen orientation:<0001>+/−0.5degree, thickness:330±25 um B Grade,MPDä30 cm-2 B Grade:RT:0.01-0.1 Ω·cmB Grade,Bow/Warp/TTV<25 um, the method including the steps of forming avapor of a polymer derived ceramic SiC, the polymer derived ceramichaving a purity of at least about 6 nines, and being oxide layer free,depositing the vapor on a seed crystal to form a boule, and providingthe boule to a wafer manufacturing process.

Thus, there is provide a method of making boule for the production of asilicon carbide wafer characterized with the properties of 2″ 6H N-Type,6H—N 2″ dia, type/dopant:N/nitrogen orientation:<0001>+/−0.5 degree,thickness:330±25 um D Grade,MPDä100 cm-2, D Grade,RT:0.02-0.2 Ω·cm, themethod including the steps of forming a vapor of a polymer derivedceramic SiC, the polymer derived ceramic having a purity of at leastabout 6 nines, depositing the vapor on a seed crystal to form a boule,and providing the boule to a wafer manufacturing process.

Still further there is provided a method of making silicon carbidewafer, the method comprising the steps of forming a vapor of a polymerderived ceramic SiC, the polymer derived ceramic having a purity of atleast about 6 nines, depositing the vapor on a seed crystal to form aboule, and providing the boule to a wafer manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 2 is a more detailed schematic cross sectional diagram of the vapordeposition apparatus of FIG. 1 utilizing ultra pure SiC or SiOCmaterials in accordance with the present inventions.

FIG. 3 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 4 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIGS. 5 a, 5 b, 5 c , are schematic cross sectional diagrams of a vapordeposition apparatus utilizing ultra pure SiC or SiOC materials inaccordance with the present inventions.

FIG. 6 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 7 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 8 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 9 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 10 is a schematic cross sectional diagram of a vapor depositionapparatus utilizing ultra pure SiC or SiOC materials in accordance withthe present inventions.

FIG. 11 is a schematic cross sectional diagram of a vapor depositionapparatus in accordance with the present inventions.

FIG. 12 is a schematic cross sectional diagram of a vapor depositionapparatus in accordance with the present inventions.

FIG. 13 is a schematic cross sectional diagram of a vapor depositionapparatus in accordance with the present inventions.

FIG. 14 a partial pressure cure for SiC, Si₂C, and SiC₂.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, the present inventions relate to vapor deposition techniquesand apparatus using polysilocarb (SiOC) and Silicon Carbide (SiC)materials having good, high, and exceedingly high purity.

Examples of vapor deposition techniques and apparatus include, forexample, CVD generally refers to Chemical Vapor Deposition. CVD is atype of vapor deposition technology. In addition to CVD, vapordeposition technologies would include PVD (Physcial Vapor Deposition),plasma enhanced CVD, Physical Vapor Transport (PVT) and others.

Generally, the present inventions are directed toward “polysilocarb”materials, e.g., material containing silicon (Si), oxygen (O) and carbon(C), and materials that have been converted to various forms of SiC fromsuch materials. Polysilocarb materials may also contain other elements.Polysilocarb materials are made from one or more polysilocarb precursorformulation or precursor formulation. The polysilocarb precursorformulation contains one or more functionalized silicon polymers, ormonomers, as well as, potentially other ingredients, such as forexample, inhibitors, catalysts, initiators, modifiers, dopants, andcombinations and variations of these and other materials and additives.Silicon oxycarbide materials, or SiOC compositions and similar terms,unless specifically stated otherwise, refer to polysilocarb materialsthat have have been cured into a plastic, or solid material containingSi, O and C, and polysilocarb materials that have been pyrolized into aceramic material containing Si, O and C.

Typically, and preferably, the polysilocarb precursor formulation isinitially a liquid. This liquid polysilocarb precursor formulation isthen cured to form a solid or semi-sold material, e.g., a plastic. Thepolysilocarb precursor formulation may be processed through an initialcure, to provide a partially cured material, which may also be referredto, for example, as a preform, green material, or green cure (notimplying anything about the material's color). The green material maythen be further cured. Thus, one or more curing steps may be used. Thematerial may be “end cured,” i.e., being cured to that point at whichthe material has the necessary physical strength and other propertiesfor its intended purpose. The amount of curing may be to a final cure(or “hard cure”), i.e., that point at which all, or essentially all, ofthe chemical reaction has stopped (as measured, for example, by theabsence of reactive groups in the material, or the leveling off of thedecrease in reactive groups over time). Thus, the material may be curedto varying degrees, depending upon its intended use and purpose. Forexample, in some situations the end cure and the hard cure may be thesame.

The curing may be done at standard ambient temperature and pressure(“SATP”, 1 atmosphere, 25° C.), at temperatures above or below thattemperature, at pressures above or below that pressure, and over varyingtime periods (both continuous and cycled, e.g., heating followed bycooling and reheating), from less than a minute, to minutes, to hours,to days (or potentially longer), and in air, in liquid, or in apreselected atmosphere, e.g., Argon (Ar) or nitrogen (N₂).

Metal alkoxides may also be used to provide metal functionality toprecursor formulations and products. Metal alkoxide compounds can bemixed with the Silicon precursor compounds and then treated with waterto form the oxides at the same time as the polymer, copolymerize. Thiscan also be done with metal halides and metal amides. Preferably, thismay be done using early transition metals along with Aluminum, Galliumand Indium, later transition metals: Fe, Mn, Cu, and alkaline earthmetals: Ca, Sr, Ba, Mg.

Compounds where Si is directly bonded to a metal center which isstabilized by halide or organic groups may also be utilized to providemetal functionality to precursor formulations and products.

Additionally, it should be understood that the metal and metal complexesmay be the continuous phase after pyrolysis, or subsequent heattreatment. Formulations can be specifically designed to react withselected metals to in situform metal carbides, oxides and other metalcompounds, generally known as cermets (e.g., ceramic metalliccompounds). The formulations can be reacted with selected metals to formin situ compounds such as mullite, alumino silicate, and others. Theamount of metal relative to the amount of silica in the formulation orend product can be from about 0.1 mole % to 99.9 mole %, about 1 mole %or greater, about 10 mole % or greater, and about 20 mole percent orgreater. The forgoing use of metals with the present precursor formulascan be used to control and provide predetermined stoichiometries.

The polysilocarb batch may also be used a binder in compositestructures, such as a binder for metal, ceramic, and inorganic matrices.

As used herein, unless specified otherwise the terms %, weight % andmass % are used interchangeably and refer to the weight of a firstcomponent as a percentage of the weight of the total, e.g., formulation,mixture, material or product. As used herein, unless specified otherwise“volume %” and “% volume” and similar such terms refer to the volume ofa first component as a percentage of the volume of the total, e.g.,formulation, material or product.

At various points during the manufacturing process, the polysilocarbstructures, intermediates and end products, and combinations andvariations of these, may be machined, milled, molded, shaped, drilled orotherwise mechanically processed and shaped.

Custom and predetermined control of when chemical reactions occur in thevarious stages of the process from raw material to final end product canprovide for reduced costs, increased process control, increasedreliability, increased efficiency, enhanced product features, increasedpurity, and combinations and variation of these and other benefits. Thesequencing of when chemical reactions take place can be based primarilyupon the processing or making of precursors, and the processing ormaking of precursor formulations; and may also be based upon cure andpyrolysis conditions. Further, the custom and predetermined selection ofthese steps, formulations and conditions, can provide enhanced productand processing features through chemical reactions, moleculararrangements and rearrangements, and microstructure arrangements andrearrangements, that preferably have been predetermined and controlled.

The ability to start with a liquid material, e.g., the precursor batch,having essentially all of the building blocks, e.g., Si and C, needed tomake SiC provides a significant advantage in controlling impurities,contamination, and in making high purity SiOC, which in turn can beconverted to high purity SiC, or which can be made directly in a singlecombined process or step. Thus, embodiments of the present inventionsprovide for the formation of SiOC that is at least about 99.9%(3-nines), at least about 99.99% (4-nines), at least about 99.999%(5-nines), and least about 99.9999% (6-nines) and at least about99.99999% (7-nines) or greater purity. Similarly, embodiments of thepresent inventions provide for the formation of SiC that is at leastabout 99.9% (3-nines), at least about 99.99% (4-nines), at least about99.999% (5-nines), and least about 99.9999% (6-nines) and at least about99.99999% (7-nines) or greater purity. These purity values are basedupon the amount of SiOC, or SiC, as the case may be, verse all materialsthat are present or contained within a given sample of SiOC or SiCproduct.

Embodiments of the present polysilocarb derived SiC and processes,reduce the cost of providing high purity and ultra high purity SiC,while also increasing the purity obtained, e.g., lower cost high puritySiC materials. Thus, among other things, embodiments of the polysilocarbSiC materials and articles have reduced costs and enhanced features,when compared to prior SiC, SiOC and Si materials and products Thus,among other things, embodiments of the polysilocarb SiC materials andarticles can replace SiC as well as Si materials and products in manyapplications, and have to ability to provide for new, additional andenhanced applications that were not obtainable with SiC and Si materialsand products for technical, economic, and both, reasons.

Embodiments of polymer derived SiC wafers include, among others, about2-inch diameter wafers and smaller, about 3-inch diameter wafers, about4-inch diameter wafers, about 5-inch diameter wafers, about 6-inchdiameter wafers, about 7-inch diameter wafers, about 12-inch diameterwafers and potentially larger, wafers having diameters from about 2inches to about 8 inches, wafers having diameters from about 4 inches toabout 6 inches, square shaped, round shaped, and other shapes, surfacearea per side of about 1 square inch, about 4 square inches, about 10square inches and larger and smaller, a thickness of about 100 μm, athickness of about 200 μm, a thickness of about 300 μm, a thickness ofabout 500 μm, a thickness of about 700 μm, a thickness from about 50 μmto about 800 μm, a thickness from about 100 μm to about 700 μm, athickness from about 100 μm to about 400 μm, and larger and smallerthickness, and combinations and variations of these.

In embodiments of the present inventions the high purity SiC has low,very and low and below detection limits, amounts of materials that causesignificant problems, or are viewed as impurities, in the laterprocessing and manufacture of items, for example, boules, wafers,electronic components, optical components and other SiC basedintermediate and end products.

Thus, polymer derived high purity SiC, and in particular polysilocarbderived high purity SiOC, as well as, the high purity SiC that the SiOCis converted into, has a purity of at least about 99.9%, at least about99.99%, at least about 99.999%, and least about 99.9999% and at leastabout 99.99999% or greater. Further, it is noted that embodiments of thepresent invention include polymer derived SiC, and SiOC, of any puritylevel, including lower levels of purity, such as 99.0%, 95%, 90% andlower. It is believe that these lower, e.g., non-high, purityembodiments have, and will find, substantial uses and applications.Similarly, it is believed that embodiments of the high purity SiC willfind applications, uses, and provide new and surprising benefits toapplications that prior to the present inventions were restricted to Sior materials other than SiC.

Embodiments of the present inventions include the use of high purity SiCin making wafers for applications in electronics and semiconductorapplications. In both the vapor deposition apparatus and processes tocreate the boules and wafers for later use, high purity SiC is required.In particular, as set forth in Table 3, embodiments of high puritypolymer derived SiOC and SiC can preferably have low levels of one, morethan one, and all elements in Table 3, which in certain vapor depositionapparatus, electronics applications, and semiconductor applications areconsidered to be impurities. Thus, embodiments of polysilocarb derivedSiC can be free of impurities, substantially free of impurities, andcontain some but have no more than the amounts, and combinations ofamounts, set out in Table 3.

TABLE 3 less than less than less than less than less than Element ppmppm ppm ppm ppm Al 1,000 100 10 1 0.1 Fe 1,000 100 10 1 0.1 B 1,000 10010 1 0.1 P 1,000 100 10 1 0.1 Pt 1,000 100 10 1 0.1 Ca 1,000 100 10 10.1 Mg 1,000 100 10 1 0.1 Li 1,000 100 10 1 0.1 Na 1,000 100 10 1 0.1 Ni1,000 100 10 1 0.1 V 1,000 100 10 1 0.1 Ti 1,000 100 10 1 0.1 Ce 1,000100 10 1 0.1 Cr 1,000 100 10 1 0.1 S 1,000 100 10 1 0.1 As 1,000 100 101 0.1 Total of one 3,000 500 50 10 1 or more of the above

In an embodiment, Pr may also be considered an impurity in someapplications and if so consider the limits and amounts of table 3 may beapplicable to Pr.

Unless specified otherwise, as used herein, when reference is made topurity levels, high purity, % purity, % impurities, and similar suchterms, excess carbon, i.e., beyond stoichiometric SiC, is not included,referenced to, considered, or used in the calculations orcharacterization of the material. In some applications excess carbon mayhave little to no effect on the application or product, and thus, wouldnot be considered an impurity. In other applications excess carbon maybe beneficial, e.g., carbon can act as a sintering aid; excess carboncan be used to address and compensate for irregularities in vapordeposition apparatus and processes.

In applications where nitrogen is viewed as a contaminate, embodimentsof polysilocarb derived SiC and SiOC can have less than about 1000 ppm,less than about 100 ppm, less than about 10 ppm, less than about 1 ppmand less than about 0.1 ppm nitrogen, and lower.

In an embodiment of the polysilocarb derived SiC it is essentially freefrom, and free from the presence of Oxygen, in any form, either bound toSi or C or as an oxide layer. Thus, embodiments of polysilocarb derivedSiC can have less than about 1000 ppm, less than about 100 ppm, lessthan about 10 ppm, less than about 1 ppm, and less than about 0.1 ppmoxygen, and lower. The polysilocarb derived SiC has the ability toresist, and does not form an oxide layer when exposed to air understandard temperatures and pressures. The absence of an oxide layer,i.e., oxide layer free SiC, under when stored under ambient conditionsprovides advantages in later manufacturing processes, where oxide layerscan be viewed as an impurity, or otherwise a detriment to themanufacturing process.

Embodiments of polysilocarb derived SiC are highly versatile materials.They can have several forms, e.g., amorphous, crystalline having manydifferent polytypes, and forming single (or mono-) and polycrystallinestructures. One, more than one, and combinations of these various forms,many be in a single batch, volumetric shape, or sample of polysilocarbderived SiC. Thus, the present polysilocarb derived SiC materials findsapplications in among other things, abrasives, friction members, optics,ballistic and impact resistant materials, insulation, and electronics.

Polysilocarb derived SiC powder, fines, pellets, or other smaller sizedand shaped forms, can be joined together by way of a sintering operationto form component parts and structures.

The joining together, e.g., pressing, sintering, ready-to-press, ofembodiments of the present polymer derived SiC can be done in anyconventional process, and can be done with the use of sintering aids andother additives that are presently used in conventional processes.Embodiments of the present ultra pure polymer derived SiC provideunique, and believed to be never before present in an SiC, abilities tohave their particles joined together without the need for any sinteringaids, or processing additives. Thus, embodiments of the present ultrapure SiC are self-sintering, being that they do not require the presenceof any sintering aids or additives in order to be joined or otherwiseformed, e.g., sintered or pressed, into a solid and preferablymonolithic solid shape. The self-sintered ultra pure SiC shapes can besignificantly stronger than a corresponding shape that was made with theuse of sintering aids. Thus, the self-sintered SiC shape can be 2×, 3×,4× or more stronger than a similar SiC shape that used sintering aids.It being theorized that the sintering aids are forming bonds orjunctures between the SiC particles and that these sintering aidjunctures are substantially weaker than the SiC-to-SiC junctures, e.g.,direct junctures, in the self-sintered shape.

Embodiments of the present polymer derived SiC, and in particular ultrapure SiC, through vapor deposition processes, crystalline growthprocesses, joining processes and other processes, can find applicationsand utilizations in among other things, broad band amplifiers, militarycommunications, radar, telecom, data link and tactical data links,satcom and point-to-point radio power electronics, LED, lasers, lightingand sensors. Additionally, these embodiments can find applications anduses in transistors, such High-electron-mobility transisitors (HEMT),including HEMT-based monolithic microwave integrated circuit (MMIC).These transistors can employ a distributed (traveling-wave) amplifierdesign approach, and with SiC's greater band gap, enabling extremelywide bandwidths to be achieved in a small footprint. Thus, embodimentsof the present inventions would include these devices and articles thatare made from or otherwise based upon polymer derived SiC.

Embodiments of the present polymer derived SiC, and in particular ultrapure SiC, through vapor deposition processes, crystalline growthprocesses, joining processes and other processes, can also findapplications and utilizations in among other things, brake rotors andassemblies, brake disks and pads, to make gemstones and semipreciousstones, jewelry, moissanite, and cutting and abrasive applications.Thus, embodiments of the present inventions would include these devicesand articles that are made from or otherwise based upon polymer derivedSiC.

Embodiments of the present polymer derived SiC, and in particular ultrapure SiC, can be combined with other ceramic power formulations toprovide enhanced benefits, reduced costs and both to processes that usesthese other ceramic powers. For example BN/SiC/ZrO2 composites, andblends with other refractory/engineering ceramic powders, e.g., AlN, BC,BN, Al2O3, ZrO2, C, SiC, WC, and SiN, to name a few are contemplated.Thus, embodiments of the present inventions would include these devicesand articles that are made from or otherwise based upon polymer derivedSiC. They may also be used in metal alloying applications, for exampleto make cermets, or other metallurgy blend and allows. For example theycan be so combined to Ti, Fe, Ni and Co, to name a few. Thus, forexample, they can form polymer derived SiC—Ti alloys, polymer derivedSiC-ferrous alloys, polymer derived SiC—Ni alloys, and polymer derivedSiC—Co alloys.

Embodiments of the present polymer derived SiC ceramic powerformulations can be utilized in, for example, as a component of, or inthe construction of: kiln furniture, furnace tubes, furnace belt links,furnace rollers, nozzles, bearings, corrosion resistant seals,crucibles, refractories, thermal protection systems, RAM-Jet/SCRAM-Jetor anything that flies above Mach 3, rockets, space shuttles, rocketnose-cones and leading edge impact protection systems, SiC/SiCreinforced composites, SiC/C reinforced composites, DC magnetronsputtering targets, thermocouple sheathing, pump seals, and valvesleeves.

Embodiments of the present polymer derived SiC, SiOC and in particularultra pure SiC and SiOC, through vapor deposition processes, crystallinegrowth processes, joining processes and other processes can findapplication and utilization in multi-layer structures, such as, forexample a layer on a substrate. This layer can be crystalline,monocrystalline, polycrystalline, or amorphous. There can be structuresthat have many varied layers, e.g., substrate layer, tie layer, SiClayer, SiOC layer, and other substances. In an embodiment sapphire canbe used as a substrate for an epitaxial SiC layer. GaN can also be anacceptable substrate. A tie layer can be used to moderate the latticemismatch between dissimilar crystalline lattice parameters. Thus, forexample where SiOC is used as a substrate it can have a tie layer tosupport SiC, or GaN layer growth on it.

In an embodiment of this process, high purity, polymer derived SiC, andpreferably very small sized, e.g., less than about 100 μm, less thanabout 10 μm, having a purity of at about 99.999%, preferably about99.9999% and more preferably about 99.99999% can be sintered intooptical components. These optical components can be transmissive toselected wavelengths, e.g., 360-800 nm. They can have indexes ofrefraction of about 2.65 in the visible spectrum. They can have good,and high optical properties, being free of aberrations, occlusions, andother optical defects. They posses the toughness (e.g., chemicalresistance, abrasion resistance, temperature resistance, hardness, ofSiC). Thus, for example, then can provide significant improvements tothe windows, or clear members, e.g., screens, on cell phones, tablets,touch screens and the like. They may be used for the bodies of thesedevices as well. These polymer derived SiC windows can be particularlyadvantageous in demanding applications, where for example, there areharsh environmental or use conditions present. They can be used in manyoptical applications, including: the generation of light, e.g., lasers,laser diodes, or other light sources; the shaping and transmitting oflight, e.g., optical fibers, windows, prisms, lens, optics, mirrors, andinternal reflectance elements (e.g., blocks, prisms that rely uponinternal reflection to direct the light).

In addition to UV, visible and IR light, the SiC optical components canfind applications in over wavelengths of electromagnetic radiation, suchas microwave, millimeter wave, x-ray, and high energy beams.

Embodiments of polysilocarb derived SiC, in particular high purity SiC,have many unique properties that, among other things, make themadvantageous and desirable for use in the electronics, solar, and powertransmission industries and applications. They can function as asemiconductor material that is very stable, and suitable for severaldemanding applications, including high power, high-frequency,high-temperature, and corrosive environments and uses. Polymer derivedSiC is a very hard material with a Young's modulus of 424 GPa. It isessentially chemically inert, and will not react with any materials atroom temperature.

Further, prior to the present inventions, it was believe that it wasessentially impossible, from all practical standpoints, to diffuseanything into silicon carbide, thus to the extent that dopants arerequired to be added to the material, they can be added by way of theprecursor and thus be present in a controlled manner and amount forgrowth into a boule, or other structure. Embodiments of precursorformulations may have dopant, or complexes that carry and bind thedopant into the ceramic and then the converted SiC, so that upon vapordeposition process the dopant is available and in a usable form.

Additionally, dopants or other additives to provide custom orpredetermined properties to wafers, layers and structures that are madefrom embodiments of the polymer derived SiC and SiOC can be used with,as a part of, or in conjunction with the present polymer derivedmaterials. In these embodiments, such property enhancing additives wouldnot be considered impurities, as they are intended to be in, necessaryto have in, the end product. The property enhancing additives can beincorporated into the liquid precursor materials. Depending on thenature of the property enhancing additive, it may be a part of theprecursor back done, it may be complexed, or part of a complex, toincorporate it into the liquid precursors, or it can be present in otherforms that will enable it to survive (e.g., be in a form that lets itfunction as intended in the final material). The property enhancingadditive can also be added as a coating to the SiC or SiOC powderedmaterial, can be added as a vapor or gas during processing, or can be inpowder form and mixed with the polymer derived SiC or SiOC particles, toname a few. Further, the form and manner in which the property enhancingadditive is present, should preferably be such that it has minimal, andmore preferably, no adverse effect on processing conditions, processingtime, and quality of the end products. Thus, a polysilocarb derived SiChaving greater than 5-nines purity, greater than 6-nines purity andgreater than 7-nines purity can have amounts of a property enhancingadditive present. These amounts can be from about 0.01% to about 50%,about 0.1% to about 5%, about 1% to about 10%, less than 25%, less than20%, less than 10% and less than 1%, as well as greater and smalleramounts depending upon the additive and the predetermined properties itis intended to impart.

Silicon carbide does not generally have a liquid phase, instead itsublimes, under vacuum, at temperatures above about 1,800° C. Turning toFIG. 10 there is provided a chart of a partial pressure curve for SiC.Typically, in industrial and commercial applications conditions areestablished so that the sublimation takes place at temperatures of about2,500° C. and above. When Silicon carbide sublimes it typically forms avapor consisting of Si, SiC, and SiC₂. Generally, it was believed thattemperature determined the ratio of these different components in theSilicon carbide vapor. The present inventions, however, among otherthings, provide the capability to preselect and control the ratio ofthese components of a SiC vapor, for example by controlling the amountof excess carbon present in the polysilocarb derived SiC. Further, byvarying, in a controlled manner, the porosity of the polysilocarbderived SiC, the amount of excess carbon present, and both (when used asa starting material in the vapor deposition process), for example, byhaving layers of SiC material having different predetermined amounts ofexcess carbon present, the make up of the Si C vapors can be varied in acontrolled manner, and varied in a control manner over time.

Polysilocarb derived SiC, and the SiC boules, wafers and otherstructures that are made from the polysicocarb derived SiC, exhibitpolymorphism, and generally a one dimensional polymorphism referred toas polytypism. Thus, polysilocarb derived SiC can be present in many,theoretically infinite, different polytypes. As used herein, unlessexpressly provided otherwise, the term polytypism, polytypes and similarsuch terms should be given their broadest possible meaning, and wouldinclude the various different frames, structures, or arrangements bywhich silicon carbide tetrahedrons (SiC₄) are configured. Generally,these polytypes fall into two categories—alpha (α) and beta (β).

Embodiments of the alpha category of polysilocarb derived SiC typicallycontains hexagonal (H), rhombohedral (R), trigonal (T) structures andmay contain combinations of these. The beta category typically containsa cubic (C) or zincblende structure. Thus, for example, polytypes ofpolysilocarb derived silicon carbide would include: 3C—SiC (β-SiC or β3C—SiC), which has a stacking sequence of ABCABC . . . ; 2H—SiC, whichhas a stacking sequence of ABAB . . . ; 4H—SiC, which has a stackingsequence of ABCBABCB . . . ; and 6H—SiC (a common form of alpha siliconcarbide, α 6H—SiC), which has a stacking sequence of ABCACBABCACB . . .. Examples, of other forms of alpha silicon carbide would include 8H,10H, 16H, 18H, 19H, 15R, 21R, 24H, 33R, 39R, 27R, 48H, and 51R.

Embodiments of polysilocarb derived SiC may be polycrystalline or single(mono-) crystalline. Generally, in polycrystalline materials there arepresent grain boundaries as the interface between two grains, orcrystallites of the materials. These grain boundaries can be between thesame polytype having different orientations, or between differentpolytypes, having the same or different orientations, and combinationsand variations of these. Mono-crystalline structures are made up of asingle polytype and have essentially no grain boundaries.

Embodiments of the present inventions provide the ability to meet thedemand for high purity silicon carbide, and in particular high puritysingle crystalline carbide materials for use in end products, such as asemiconductors. Thus, for these end products, and uses, which requirehigh purity materials, it is desirable to have a low cost siliconcarbide raw material that has a purity of at least about 99.9%, at leastabout 99.99%, at least about 99.999%, and least about 99.9999% and atleast about 99.99999% or greater.

High purity single crystalline silicon carbide material has manydesirable features and characteristics. For example, it is very hardhaving a Young's modulus of 424 GPa. Polycrystalline silicon carbide mayalso have very high hardness, depending upon its grain structure andother factors.

Embodiments of the present polysilocarb derived SiC would include theability to provide larger diameter or cross section (e.g., about 5inches, greater than 5 inches, about 6 inches, greater than 7 inches,about 8 inches, greater than 8 inches, greater than 9 inches, about 12inches, and greater) seed crystals, boules and other structures. Suchlarger diameter or cross section structures can preferably have a purityof at least about 99.9%, at least about 99.99%, at least about 99.999%,and least about 99.9999% and at least about 99.99999% or greater.

Embodiments of the present inventions include articles, e.g.,semiconductors, of silicon carbide having a band gap that varies bypolytype between 2.39 eV for (beta SiC) 3C—SiC to 3.33 eV for 2H—SiC.4H—SiC has a band gap of 3.265 eV. Alpha silicon carbide (6H—SiC) has aband gap of 3.023 eV. These band gaps are larger than for Si, which hasa band gap of 1.11 eV. The high band gap allows silicon carbidematerials to work in sensors, e.g., a gas sensor, that are operated inhigh temperature, e.g., up to about 1,000° C., environments. Forexample, a silicon carbide based gas sensor can have response times ofonly a few milliseconds while operating in temperatures of about 1,000°C.

Embodiments of materials made from polymer derived SiC, SiOC, and inparticular high purity polymer derived SiC and SiOC, can be utilized inpower devices and power device applications. For power deviceapplications, the breakdown electric field strength E_(max) can be animportant property. This property quantizes how high the largest fieldin the material may be before material breakdown occurs (e.g.,catastrophic breakdown). The E_(max) is dependent upon doping levels,but in general for a SiC material and a Si material having the samedoping levels the SiC E_(max) can be on the order of 4 to 10 timesgreater. E_(max) and relative E_(max) can also be viewed from theperspective of the relative strengths of a device constructed to havethe same blocking voltage. Thus, an Si device constructed for a blockingvoltage of I kV would have a critical field strength of about 0.2 MV/cm,and a similar SiC device would have a critical field strength of about2.49 MV/cm.

Embodiments of materials made from polymer derived SiC, SiOC, and inparticular high purity polymer derived SiC and SiOC, can be utilized inhigh frequency devices and high frequency applications. Saturation driftvelocity can be an important property for high frequency devices.Silicon carbide has a saturation drift velocity of 2×10⁷ cm/sec², whilea similar silicon's saturation drift velocity is about half of that.High saturation drift velocities are advantageous, if not necessary, forhigh-gain solid state devices. Thus, with embodiments of the presentinventions providing high purity, low cost (e.g., cost effective)silicon carbide, it now can become a preferred choice from a materialsperspective for such devices. However, it is believed that it was achoice that generally the art would not make, prior to the presentinventions, because of the costs associated with utilizing siliconcarbide; and the difficulty, if not impossibility in obtaining theneeded purity.

Embodiments of materials made from polymer derived SiC, SiOC, and inparticular high purity polymer derived SiC and SiOC, can be utilized inhigh thermal conductivity applications. The thermal conductivity ofsilicon carbide is higher than that of copper at room temperature, andit is believe may be superior to most if not all metals. For example thethermal conductivity of silver is 4.18 W/(cm-K), and of copper is 4.0W/(cm-K) at room temperature. High purity silicon carbide can havethermal conductivity of greater than about 4.0 W/(cm-K), greater thanabout 4.5 W/(cm-K), about 4.9 W/(cm-K), and greater at room temperature.

Embodiments of the present inventions, and the advances in SiCprocessing and materials provided by the present inventions, can replacesilicon materials, in many, the majority, if not essentially allelectronics and other applications; as well as additional and new,applications and uses beyond conventional silicon based semiconductorand electrons applications.

Embodiments of polysilocarb derived high purity SiC, e.g., having apurity of at least about 99.9%, at least about 99.99%, at least about99.999%, and least about 99.9999% and at least about 99.99999% orgreater, can have many different polytypes. The polysilocarb derivedhigh purity SiC and SiOC may be present as alpha (α), beta (β) andcombinations and variations of these. Embodiments of the alpha categoryof polysilocarb derived high purity SiC typically contains hexagonal(H), rhombohedral (R), trigonal (T) structures and may containcombinations of these. The beta category of polysilocarb derived highpurity SiC typically contains a cubic (C) or zincblende structure. Thus,for example, polytypes of polysilocarb derived high purity siliconcarbide would include: 3C—SiC (β-SiC or β3C—SiC); 2H—SiC; 4H—SiC; and6H—SiC (a common form of alpha silicon carbide, α 6H—SiC), which has astacking sequence of ABCACBABCACB . . . . Examples, of other forms ofalpha silicon carbide would include 8H, 10H, 16H, 18H, 19H, 15R, 21R,24H, 33R, 39R, 27R, 48H, and 51R. Embodiments of polysilocarb-derivedhigh purity SiC can be polycrystalline or single (mono-) crystalline.High purity SiOC, and SiOC derived SiC may be in an amorphous form.

Embodiments of the present inventions have the ability to provide, andare, high purity SiOC and SiC in the form of volumetric structures,e.g., pucks, briquettes, bricks, blocks, tablets, pills, plates, discs,squares, balls, rods, random shapes, etc. These volumetric shapes have awide range of sizes, generally from about 1/16 in³ to about 1 ft³,although larger and smaller volumes are contemplated. Embodiments of thevolumetric structures can be very soft, and crumbly, or friable,preferably having the ability to fall apart with average hand pressure.Thus, these friable SiC volumetric structures can have: an elasticmodulus of less than about 200 GPa, less than about 150 GPa, less thanabout 75 GPa, and less than about 10 GPa and smaller; a hardness of lessthan about 1,400 Kg/mm² less than about 800 Kg/mm², less than about 400Kg/mm², less than about 100 Kg/mm² and smaller; and, compressivestrength of less than about 1,850 MPa, of less than about 1,000 MPa ofless than about 750 MPa, of less than about 200 MPa, of less than about50 MPa, and smaller. Thus, these friable SiC volumetric shapes aresubstantially weaker than their underlying SiC material that makes uptheir structure, and which has reported values of elastic modulus ofabout 410 GPa, hardness of about 2,800 Kg/mm² and compressive strengthof about 3,900 MPa. The actual density of the SiC, measured by HeliumPycnometry, is from about 3.0 to 3.5 g/cc, or about 3.1 to 3.4 g/cc, orabout 3.2 to 3.3 g/cc. The apparent density, or specific gravity, forthe friable volumetric shapes of SiC, e.g., pellets, pills, etc., may besignificantly lower.

The mass of SiC (e.g., volumetric shape of the granular SiC particles,friable mass) preferably, and typically, has an apparent density that isconsiderably lower, than its actual density, e.g., actual density of anSiC granule should be about 3.1 g/cc to 3.3 g/cc. In general, andtypically, the apparent and actual density of the granular SiC that isobtained from crushing the friable mass are essentially identical. Theapparent density for the friable mass (e.g. a puck, pellet, disk orplate) can be less than about 3 g/cc, less than about 2 g/cc. less thanabout 1 g/cc and lower, and can be from about 0.5 g/cc to about 1.5g/cc, about 0.4 g/cc to about 2 g/cc. The bulk density for particles ofthe SiC can be less than about 3.0 g/cc, less than about 2.0 g/cc, lessthan about 1 g/cc, and from about 0.1 g/cc to about 2 g/cc, 0.5 g/cc toabout 1.5 g/cc. Greater and lower apparent densities and bulk densitiesare also contemplated. Moreover, specific, i.e., predetermined andprecise, apparent densities for a friable mass of polymer derived SiCcan be provided to match, and preferably enhance and more preferableoptimize, later manufacturing processes. For example, in CVD wafermaking, the friable mass of SiC granules can have an apparent densitythat is specifically designed and tailored to match a specific CVDapparatus. In this manner, each CVD apparatus in a facility can havecustom feed stock, which enables each apparatus' performance to beoptimized by the use of the feed stock (e.g., the friable mass of SiC)having a predetermined and precise apparent density.

The friable SiC volumetric shapes can thus be easily and quickly brokendown into much smaller particles of SiC, having the typical strengthcharacteristics of SiC. The smaller particles can be less than about 10mm in diameter, less than about 1 mm in diameter, less than about 0.01mm in diameter, less than about 100 μm (microns) in diameter, less thanabout 10 μm in diameter, and less than about 1 μm, less than about 500nm (nanometers), to less than about 100 nm it being understood thatsmaller and larger sizes are contemplated.

Thus, embodiments of the present invention provide for the formation ofa friable mass or volumetric shape of SiC, from a SiOC precursor, andfrom this friable mass of SiC obtain granular SiC. The granular SiChaving significantly greater strength than the bulk properties of thefriable mass of SiC. For example, the granular SiC can have an elasticmodulus that is about 2× greater than the mass of SiC, about 3× greaterthan the mass of SiC, about 4× greater than the mass of SiC, andgreater; the granular SiC can have a hardness that is about 2× greaterthan the mass of SiC, about 3× greater than the mass of SiC, about 4×greater than the mass of SiC, and greater; the granular SiC can have ancompressive strength that is about 2× greater than the mass of SiC,about 3× greater than the mass of SiC, about 4× greater than the mass ofSiC, and greater; and combinations and variation of these increasedstrength related features.

The friable mass of SiC that is obtained from for example the process ofthe embodiment of FIG. 1 (e.g., 103c of segment 108) can be reduced togranular SiC with crushing equipment such as a ball mill, an attritionmill, a rotor stator mill, a hammer mill, a jet-mill, a roller mill, abead mill, a media mill, a grinder, a homogenizer, a two-plate mill, adough mixer, and other types of grinding, milling and processingapparatus.

The friable mass of SiC has an inherent porosity to it. This porosity ispreferably open hole, or substantially open hole porosity. In thismanner, the friable mass typically provides substantially greateravailable surface area than granular SiC, because the granules arepacked against one another. Thus, for example, if a friable discs of SiCwere used in a vapor deposition process to make SiC boules (forsubsequent conversion into SiC wafers), these friable SiC discs wouldprovide substantially greater surface area from which to create SiCvapor, and substantially greater paths for movement of the SiC vapor,than could typically be obtained from using granular SiC in such aprocess. It is theorized that the increase surface area and theincreased pathways, provides the ability to increase the rate of growthof the SiC boule, the quality of the SiC boule (and thus the subsequentwafers) and both of these. The friable SiC discs, e.g., the mass of SiC,may be easier to handle, measure, and use than the granular SiCmaterial.

The friable mass of SiC preferably, and typically, has an apparentdensity that is considerably lower, than its actual density, e.g.,actual density should be about 3.2 g/cc. In generally, the granular SiC,which is obtained from crushing the friable mass, has an apparent andactual density that are essentially identical, e.g., about 3.1 to 3.3g/cc.

The force required to break up the friable mass of SiC to a granularform is minimal, compared to the force that was needed with conventionalmethods of making SiC (e.g., by carbothermal reduction of silica,Acheson type or based). The conventional methods, typically produce abatch of SiC in a monolith, having the strength of SiC, and whichtypically must be granulized, e.g., ground, cut, shaved, or milled, downto useful sizes. Thus, embodiments of the present inventions avoid theneed for such heavy or robust grinding equipment to granulize themonolith of SiC. They further avoid the high cost of power, e.g.,electricity, to operate such grinding equipment. They also greatlyreduce the time need to granulize the SiC. It could take upwards ofweek(s), using this heaving grinding equipment, to granulize themonolith SiC to a useful size. While, an embodiment of the friable massof SiC of the present inventions can be granulized in only a few hours,an hour, less than an hour, less than 30 minutes, a few minutes, andless. This grinding process for example can be, for example, postprocessing segment.

The features of the high purity polysicocarb SiC provide severaladvantages and benefits for use in, e.g., as the Si and C source orstarting material, vapor deposition processes, systems and apparatus,among other techniques for growing or creating a SiC mass, structure,article or volumetric shape. These features include: the ability to havehigh purity levels, a high purity levels, the ability to controlparticle size distribution (shape, size and both); predeterminedparticle size distribution; the ability to have volumetric shapes;predetermined volumetric shapes (e.g., pucks, pills, discs, etc.); theability to have porosity and control porosity; predetermined porosity;the ability to control the amount of carbon; predetermined carbonamounts (both excess, i.e., greater than stoichiometric, starved, i.e.,less than stoichiometric and stoichiometric); and combinations andvariations of these and other properties. While additional advantagesfor the present inventions may be seen, presently and by way of example,these advantages in vapor deposition processes would include shorteningthe time to grow the boule or other structure, longer run times beforecleaning, the ability to optimize an apparatus, the ability to growlarger diameter boules or other structures, the ability to increasequality, the ability to reduce problematic areas, problematic regions orproblematic occurrences (e.g., pipes, occlusions, imperfections) fromthe boule or other structure, reduced costs, greater control over theprocess, and combinations and variations of these.

It should be understood that the use of headings in this specificationis for the purpose of clarity, and is not limiting in any way. Thus, theprocesses and disclosures described under a heading should be read incontext with the entirely of this specification, including the variousexamples. The use of headings in this specification should not limit thescope of protection afford the present inventions.

Typically polymer derived ceramic precursor formulations, and inparticular polysilocarb precursor formulations can generally be made bythree types of processes, although other processes, and variations andcombinations of these processes may be utilized. These processesgenerally involve combining precursors to form a precursor formulation.One type of process generally involves the mixing together of precursormaterials in preferably a solvent free process with essentially nochemical reactions taking place, e.g., “the mixing process.” The othertype of process generally involves chemical reactions, e.g., “thereaction type process,” to form specific, e.g., custom, precursorformulations, which could be monomers, dimers, trimers and polymers. Athird type of process has a chemical reaction of two or more componentsin a solvent free environment, e.g., “the reaction blending typeprocess.” Generally, in the mixing process essentially all, andpreferably all, of the chemical reactions take place during subsequentprocessing, such as during curing, pyrolysis and both.

It should be understood that these terms—reaction type process, reactionblending type process, and the mixing type process—are used forconvenience and as a short hand reference. These terms are not, andshould not be viewed as, limiting. For example, the reaction process canbe used to create a precursor material that is then used in the mixingprocess with another precursor material.

These process types are described in this specification, among otherplaces, under their respective headings. It should be understood thatthe teachings for one process, under one heading, and the teachings forthe other processes, under the other headings, can be applicable to eachother, as well as, being applicable to other sections, embodiments andteachings in this specification, and vice versa. The starting orprecursor materials for one type of process may be used in the othertype of processes. Further, it should be understood that the processesdescribed under these headings should be read in context with theentirely of this specification, including the various examples andembodiments.

Preferred SiOC Derived SiC Curing and Pyrolysis

Preferably, in making SiC, and materials for use in making SiC, in apreferred embodiment the polysilocarb precursors can be mixed at about 1atmosphere, in cleaned air.

Preferably, in making SiC, and materials for use in making SiC, thecuring takes place at temperatures in the range of from about 20° C. toabout 150° C., from about 75° C. to about 125° C. and from about 80° C.to 90° C. The curing is conducted over a time period that preferablyresults in a hard cured material. The curing can take place in air or aninert atmosphere, and preferably the curing takes place in an argonatmosphere at ambient pressure. Most preferably, for high puritymaterials, the furnace, containers, handling equipment, and othercomponents of the curing apparatus are clean, essentially free from, anddo not contribute any elements or materials, that would be consideredimpurities or contaminants, to the cured material.

Preferably, in making SiC, and materials for use in making SiC, thepyrolysis takes place at temperatures in the range of from about 800° C.to about 1300° C., from about 900° C. to about 1200° C. and from about950° C. to 1150° C. The pyrolysis is conducted over a time period thatpreferably results in the complete pyrolysis of the preform. Preferablythe pyrolysis takes place in inert gas, e.g., argon, and more preferablyin flowing argon gas at or about at atmospheric pressure. The gas canflow from about 1,200 cc/min to about 200 cc/min, from about 800 cc/minto about 400 cc/min, and at about 500 cc/min. Preferably, an initialvacuum evacuation of the processing furnace is completed to a reducedpressure at least below 1E-3 Torr and re-pressurized to greater than 100Torr with inert gas, e.g., Argon. More preferably, the vacuum evacuationis completed to a pressure below 1E-5 Torr prior to re-pressurizing withinert gas. The vacuum evacuation process can be completed anywhere fromzero to >4 times before proceeding. Most preferably, for high puritymaterials, the furnace, containers, handling equipment, and othercomponents of the curing apparatus are clean, essentially free from,free from and do not contribute any elements or materials, that would beconsidered impurities or contaminants, to the cured material.

In embodiments where low N and O levels are required, the use of avacuum, preferably a turbopump, to achieve 10E-6 Torr and backfillingwith inert gas is preferable. This purging process can be done once, ormultiple times, to achieve low levels. A constant flow rate of“sweeping” gas can help purge the furnace during volatile generation.

Preferably, in making SiC, the ceramic SiOC is converted to SiC insubsequent or continued pyrolysis or conversion steps. The conversionstep from SiOC may be a part of, e.g., continuous with, the pyrolysis ofthe SiOC preform, or it may be an entirely separate step in time,location and both. Depending upon the type of SiC desired the conventionstep can be carried out from about 1,200° C. to about 2,550° C. and fromabout 1,300° C. to 1,700° C. Generally, at temperatures from about1,600° C. to 1900° C., the formation of beta types is favored over time.At temperatures above 1900° C., the formation of alpha types is favoredover time. Preferably the conversion takes place in an inert gas, e.g.,argon, and more preferably in flowing argon gas at or about atatmospheric pressure. The gas can flow from about 600 cc/min to about 10cc/min, from about 300 cc/min to about 50 cc/min, and at about 80 cc/minto about 40 cc/min. Most preferably, for high purity materials, thefurnace, containers, handling equipment, and other components of thecuring apparatus are clean, essentially free from, and do not contributeany elements or materials, that would be considered impurities orcontaminants, to the SiC.

The subsequent yields for SiOC derived SiC are generally from about 10%to 50%, typically from 30% to 40%, although higher and lower ranges maybe obtained.

Most preferably, when making high purity SiC, the activities associatedwith making, curing, pyrolizing and converting the material areconducted in, under, clean room conditions, e.g., under an ISO 14644-1clean room standard of at least ISO 5, of at least ISO 4, of at leastISO 3, of at least ISO 2, and at least ISO 1. In an embodiment thematerial handling steps are conducted in the cleanroom of at least ISO5, while a less clean area (ISO>5) is used for the pyrolysis andconversion steps.

The use of ultra pure polymer derived SiC in vapor deposition techniquesprovides superior quality, and reduce defects in the boules, wafers andsemiconductors that are made from these ultra pure polymer derivedmaterials when compared to boules and wafers made from other sources ofSiC, i.e., non-polymer derived ceramic based SiC. While not being boundby the present theory, it is believed that the polymer derived ceramicprocesses used to obtain ultra pure SiC from liquid SiOC startingmaterials, e.g., polysilocarb precursors, provides starting raw materialSiC that has different features, and morphology, from other sources ofSiC, which differences permit the polymer derived ceramic material topreform significantly better than other sources of SiC. When polymerderived ceramic SiC is used as a seed crystal it is believed thatadditional enhancements in boule and wafer qualities and efficiencies ofmanufacturing can be achieved over other SiC seed crystals. Thesebenefits and improve features include enhancements and improvements, inat least the following properties and features and/or the reduction ofat least the following deleterious properties or effects:

Bow—a measure of concave or convex deformation of the median surface ofa wafer, independent of any thickness variation which may be present.Bow is determined at the center point of the wafer with respect to areference plane determined by three points equally spaced on a circlewhose diameter is 6.35 mm less than the nominal wafer diameter. Bow is abulk property of the wafer, not a property of an exposed surface.Generally, bow is determined with the wafer in a free, unclampedposition. (Not to be confused with warp.)

Diameter—the linear distance across a circular silicon wafer whichincludes the wafer center and excludes any flats or other peripheralfiducial areas.

Edge contour—the cross sectional profile of a wafer edge shaped bygrinding or etching. Edges may be either rounded or beveled.

Flatness—for wafer surfaces, the deviation of the front surface,expressed as TIR or maximum FPD, relative to a specified reference planewhen the back surface of the wafer is ideally flat, as when pulled downby vacuum onto an ideally clean flat chuck. The flatness of a wafer maybe described as: the global flatness; the maximum value of site flatnessas measured on all sites; or the percentage of sites which have a siteflatness equal to or less than a specified value.

Flatness quality area—that portion of the surface of a wafer over whichthe specified flatness values apply. The flatness quality area is mostfrequently defined with an edge exclusion area, a peripheral annulususually 3 mm wide.

Focal plane—the plane perpendicular to the optical axis of an imagingsystem which contains the focal point of the imaging system.

Focal plane deviation (FPD)—the distance parallel to the optical axisfrom a point on the wafer surface to the focal plane. globalflatness—the TIR or maximum FPD within the flatness quality arearelative to a specified reference plane.

Maximum FPD—the largest of the absolute values of the focal planedeviations.

Primary flat—the flat of longest length which is oriented with respectto a specific crystallographic plane. Also known as major flat.

Reference plane—a plane specified by one of the following: three pointsat specified locations on the front surface of the wafer; the leastsquares fit to the front surface of the wafer using all points withinthe flasness quality area; the least squares fit to the front surface ofthe wafer using all points within a site; or an ideal back surface(equivalent to the ideally flat chuck surface that contacts the wafer).

Secondary flat(s)—the flat or flats of a length shorter than that of theprimary flat whose angular position with respect to the primary flatidentifies the conductivity type and orientation of the wafer. Alsoknown as minor flat.

Site—a rectangular area, on the front surface of the wafer, whose sidesare parallel with and perpendicular to the primary flat and whose centerfalls within the flatness quality area.

Site flatness—the TIR or maximum FPD of the portion of a site whichfalls within the flatness quality area.

Thickness—the distance through the wafer between corresponding points onthe front and back surface.

Total indicator reading (TIR)—the smallest perpendicular distancebetween two planes, both parallel with the reference plane, whichenclose all points within a specified flatness quality area or site onthe front surface of a wafer.

Total thickness variation (TTV)—the difference between the maximum andminimum thickness values encountered during a scan pattern or a seriesof point measurements on a wafer.

Warp—the difference between the maximum and minimum distances of themedian surface of the wafer from a reference plane encountered during ascan pattern. Warp is a bulk property of the wafer, not a property of anexposed surface. The median surface may contain regions with upward ordownward curvature or both. Generally, warp is determined with the waferin a free, unclamped position. (Not to be confused with bow.)

Utodoping—dopant, from sources other than the dopant intentionally addedto the vapor phase, which is incorporated into an epitaxial layer duringgrowth.

Autodoping barrier—a film or layer which impedes transport of impurityatoms from the back surface of a substrate to the epi layer duringepitaxial deposition. Also known as backseal.

Conductivity type—defines the nature of the majority of the carriers insilicon: n-type material, in which electrons are the majority carrier,is formed when a donor dopant impurity is added to the silicon; p-typematerial, in which holes are the majority carrier, is formed when anacceptor dopant impurity is added to the silicon.

Crystal orientation—the crystallographic axis, on which the siliconcrystal is grown.

Dislocation—a line imperfection in a crystal which forms the boundarybetween slipped and nonslipped regions of the crystal.

Dislocation density—the number of dislocation etch pits per unit area onan exposed wafer surface.

Dislocation etch pit—a sharply defined depression in the immediateregion of a stressed or defective crystal lattice, resulting frompreferential etching.

Dopant—a chemical element from the third (such as boron) or fifth (suchas phosphorus or antimony) column of the periodic table, intentionallyincorporated into a silicon crystal in trance amounts to establish itsconductivity type and resistivity. P-Type Bor 0.001-50 ohmcm. N-TypePhosphorus 0.1-40 ohmcm Antimony 0,005-0,025 ohmcm Arsenic <0.005 ohmcm.

Extrinsic gettering—controlled damage or stress to the crystal latticestructure intentionally introduced by mechanical means or by depositionof a polysilicon or other film on the back surface of a silicon wafer.

Flat orientation (primary)—the crystallographic plane, which ideallycoincides with the surface of the primary flat, The primary flat isusually a <110> plane.

Miller indices—the reciprocals of the intercepts of a crystallographicplane with the x-, y-, and z-axes, respectively. For example, the cubeface perpendicular to the x-axis is the <100> plane. A family of planesis denoted by curly brackets; e.g., all cube faces are the <100> planes.Directions are denoted by Miller indices in square brackets; e.g., thex-axis is the <100> direction an the cube diagonal is the <111>direction. Families of directions are denoted by angular brackets; e.g.,all cubic axes are the <100> directions. A negative direction is denotedby a minus sign over the index; e.g., the negative x-axis is the < 100>direction.

Polycrystalline silicon (polisilicon, poly)-silicon made up of randomlyoriented crystallites and containing large-angle grain boundaries, twinboundaries, or both.

Radial oxygen variation—the difference between the average oxygenconcentration at one or more points symmetrically located on a siliconwafer and the oxygen concentration at the center of the wafer, expressedas a percent of the concentration at the center. Unless otherwisespecified, Siltec considers the radial oxygen variation to be determinedusing the average of the oxygen concentrations at the two points 10 mmfrom the edge of the wafer. Radial oxygen variation is sometimesdetermined using the average of the oxygen concentrations at severalsymmetric points half way between the center and the edge of the wafer.Also known as oxygen gradient.

Radial resistivity variation—the difference between the averageresistivity at one or more points symmetrically located on a siliconwafer and the resistivity at the center of the wafer, expressed as apercent of the resistivity at the center, Unless otherwise specified, weconsider the radial resistivity variation to be determined using theaverage resistivity of four points 6 mm from the edge of the wafer ontwo perpendicular diameters. Radial resistivity variation is sometimesdetermined using the average of the resistivity at the four point halfway between the center and the edge of the wafer on the same diameters.Also known as resistivity gradient.

Resistivity (ohm·cm)—the ratio of the potential gradient (electricfield) parallel with the current to the current density, In silicon, theresistivity is controlled by adding dopant impurities; lower resistivityis achieved by adding more dopant.

Slip—a process of plastic deformation in which one part of a crystalundergoes a shear displacement relative to another in a fashion whichpreserves the crystallinity of the silicon. After preferential etching,slip is evidenced by a pattern of one or more parallel straight lines of10 or more dislocation etch pits per millimeter which do not necessarilytoch each other. On <111> surfaces, groups of lines are inclined at 60°to each other; on <100> surfaces, they are inclined at 90° to eachother.

Stacking fault—a two-dimensional defect resulting from a deviation fromthe normal stacking sequence of atoms in a crystal. It may be present inthe bulk crystal, grow during epitaxial deposition (usually as a resultof a contaminated or structurally imperfect substrate surface); ordevelop during oxydation. On <111> surfaces, stacking faults arerevealed by preferential etching either as closed or partial equilateraltriangles. On <100> surfaces, stacking faults are revealed as closed orpartial squares.

Striations—helical features on the surface of a silicon wafer associatedwith local variations in impurity concentration. Such variations areascribed to periodic differences in dopant incorporation occurring atthe rotating solid-liquid interface during crystal growth. Striationsare visible to the unaided eye after preferential etching and appear tobe continuous under 100× magnification.

Subsurface damage—residual crystallographic imperfections apparent onlyafter preferential etching of the polished silicon surface. Such damageis usually considered to be caused by mechanical processing of thewafer.

Twinned crystal—a crystal in which the lattice consists of two partsrelated to each other in orientation as mirror images across a coherentplanar interface known as the twinning plane or twin boundary, Insilicon, this plane is a <111> plane. Also known as twin.

Wafer orientation—the crystallographic plane, described in terms ofMiller indices, with which the surface of the wafer is ideallycoincident. Generally, the surface of the wafer corresponds within a fewdegrees with the low index plane perpendicular to the growth axis. Insuch cases, the orientation may also be described in terms of theangular deviation a of the low-index crystallographic plane from thepolished wafer surface.

Chip—region where material has been removed from the surface or edge ofthe wafer. The size of a chip is defined by its maximum radial depth andperipheral chord length as measured on an orthographic shadow projectionof the specimen outline. Also known as clamshell, conchoidal fracture,edge chip, flake, nick, peripheral chip, peripheral indent, and surfacechip.

Contamination—abroad category of foreign matter visible to the unaidedeye on the wafer surface. In most cases, it is removable by gas blowoff, detergent wash, or chemical action. See also particulatecontamination, stain.

rack—cleavage that extends to the surface of a wafer and which may ormay not pass through the entire thickness of the wafer. Also known asfissure; see also fracture.

Cratering—a surface texture of irregular closed ridges with smoothcentral regions. crow's-foot—intersecting cracks in a pattern resemblinga “crow's foot” (Y) on <111> surfaces and a cross (+) on <100> surfaces.

Dimple—a smooth surface depression, larger than 3 mm in diameter, on awafer surface.

Fracture—a crack with single or multiple lines radiating from a point.

Groove—a shallow scratch with rounded edges, usually the remnant of ascratch not completely removed during polishing.

Haze—a cloudy or hazy appearance attributable to light scattering byconcentrations of microscopic surface irregularities such as pits,mounds, small ridges or scratches, particles, etc.

Imbedded abrasive grains—abrasive particles mechanically forced into thesurface of the silicon wafer. This type of contamination may occurduring slicing, lapping, or polishing.

Indent—an edge defect that extends from the front surface to the backsurface of the silicon wafer.

Light point defects (LPD)—individual fine points of reflected light seenwhen the wafer is illuminated by a narrow-beam light source heldperpendicular to the wafer surface.

Mound—irregularly shaped projection with one or more facets. Mounds canbe extensions of the bulk material or various forms of contamination, orboth. A high density of mounds can also appear as haze.

Orange peel—a large-featured, roughened surface, similar to the skin ofan orange, visible to the unaided eye under fluorescent light but notusually under narrow-beam illumination.

Particulate contamination—a form of contamination comprising particles,such as dust, lint, or other material resting on the surface of thewafer and standing out from the surface. May usually be blown off thesurface with clean, dry nitrogen.

Pit—a depression in the surface where the sloped sides of the depressionmeet the wafer surface in a distinguishable manner (in contrast to therounded sides of a dimple).

Saw blade defect—a roughened area visible after polishing with a patterncharacteristic of the saw blade travel. It may be discernible beforechemical polishing. Also known as saw mark.

Scratch—a shallow groove or cut below the established plane of thesurface, with a length-to-width ratio greater than 5:1. A macroscratchis =0.12 μm in depth and is visible to the unaided eye under bothincandescent (narrow-beam) and fluorescent illumination. A microscratchis <0.12 μm in depth and is not visible to the unaided eye underflourescent illumination.

Spike—a tall, thin dendrite or crystalline filament which often occursat the center of a recess in the surface of an epitaxial layer.

Stain—a form of contamination such as a streak, smudge, or spot whichcontains foreign chemical compounds such as organics or salts.

Wafers having the following features can be made with the polymerderived ultra pure SiC materials.

Type Description 2″ 6H N- 6H—N 2″ dia, Type/Dopant: N/Nitrogen TypeOrientation: <0001> +/− 0.5 degree Thickness: 330 ± 25 um D Grade,MPDä100 cm−2 D Grade, RT: 0.02-0.2 Ω · cm Single face polished/Si faceepi-ready with CMP, Surface Roughness: <0.5 nm 2″ 6H N- 6H—N 2″ dia,Type/Dopant: N/Nitrogen Type Orientation: <0001> +/− 0.5 degreeThickness: 330 ± 25 um B Grade, MPDä30 cm−2 B Grade, RT 0.02~0.2 Ω · cmSingle face polished/Si face epi-ready with CMP, Surface Roughness: <0.5nm 2″ 4H N- 4H—N 2″ dia, Type/Dopant: N/Nitrogen Type Orientation:<0001> +/− 0.5 degree Thickness: 330 ± 25 um D Grade, MPDä100 cm−2 DGrade: RT: 0.01-0.1 Ω · cm D Grade, Bow/Warp/TTV <25 um Single facepolished/Si face epi-ready with CMP, Surface Roughness: <0.5 nm 2″ 4H N-4H—N 2″ dia, Type/Dopant: N/Nitrogen Type Orientation: <0001> +/− 0.5degree Thickness: 330 ± 25 um B Grade, MPDä30 cm−2 B Grade: RT: 0.01-0.1Ω · cm B Grade, Bow/Warp/TTV <25 um Single face polished/Si faceepi-ready with CMP, Surface Roughness: <0.5 nm 3″ 4H N- 4H—N 3″ dia,Type/Dopant: N/Nitrogen Type Orientation: 4 degree +/− 0.5 degreeThickness: 350 ± 25 um D Grade, MPDä100 cm−2 D Grade, RT: 0.01-0.1 Ω ·cm D Grade, Bow/Warp/TTV <35 um Double face polished/Si face epi-readywith CMP, Surface Roughness: <0.5 nm 3″ 4H N- 4H—N 3″ dia, Type/Dopant:N/Nitrogen Type Orientation: 4 degree +/− 0.5 degree Thickness: 350 ± 25um B Grade, MPDä30 cm−2 B Grade, RT: 0.01-0.1 Ω · cm B Grade,Bow/Warp/TTV <35 um Double face polished/Si face epi-ready with CMP,Surface Roughness: <0.5 nm 3″ 4H SI 4H—SI 3″ dia, Type/Dopant:Semi-insulating/V Orientation: <0001> +/− 0.5 degree Thickness: 350 ± 25um D Grade, MPDä100 cm−2 D Grade, RT: 70% ≥ 1E5 Ω · cm Double facepolished/Si face epi-ready with CMP, Surface Roughness: <0.5 nm 3″ 4H SI4H—SI 3″ dia, Type/Dopant: Semi-insulating/V Orientation: <0001> +/− 0.5degree Thickness: 350 ± 25 um B Grade, MPDä30 cm−2 B Grade, RT: 80% ≥1E5 Ω · cm Double face polished/Si face epi-ready with CMP, SurfaceRoughness: <0.5 nm 2″ 6H SI 6H—SI 2″ dia, Type/Dopant: Semi-insulating/VOrientation: <0001> +/− 0.5 degree Thickness: 330 ± 25 um D Grade,MPDä100 cm−2 D Grade, RT: 70% ≥ 1E5 Ω · cm Single face polished/Si faceepi-ready with CMP, Surface Roughness: <0.5 nm 2″ 6H SI 6H—SI 2″ dia,Type/Dopant: Semi-insulating/V Orientation: <0001> +/− 0.5 degreeThickness: 330 ± 25 um B Grade, MPDä30 cm−2 B Grade, RT: 85% ≥ 1E5 Ω ·cm Single face polished/Si face epi-ready with CMP, Surface Roughness:<0.5 nm 4″ 4H N- 4H—N 4″dia. (100 mm ± 0.38 mm), Type/Dopant: N/NitrogenType Orientation: 4.0° ± 0.5° Thickness: 350 μm ± 25 μm D Grade, MPDä100cm−2 D Grade, 0.01~0.1 Ω · cm D Grade, TTV/Bow/Warp <45 um Double facepolished/Si face epi-ready with CMP, Surface Roughness: <0.5 nm SSP =Single Side Polished, DSP = Double Side Polished, E = Etched, C = AsCut,Material - CZ unless noted, L = Lapped, Und = Undoped (Intrinsic)

This Group includes single crystal silicon grown by both the Czochralski(Cz) and Floating Zone (Fz) techniques

The following examples are provided to illustrate various embodimentsof, among other things, precursor formulations, processes, methods,apparatus, articles, compositions, and applications of the presentinventions. These examples are for illustrative purposes, and should notbe viewed as, and do not otherwise limit the scope of the presentinventions. The percentages used in the examples, unless specifiedotherwise, are weight percent of the total batch, preform or structure.

EXAMPLES Example 1

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together, at room temperature, 41% MHFand 59% TV. This precursor formulation has 0.68 moles of hydride, 0.68moles of vinyl, and 1.37 moles of methyl. The precursor formulation hasthe following molar amounts of Si, C and O based upon 100 g offormulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.37 25% C 2.74 50% O 1.37 25%

As calculated, the SiOC derived from this formulation will have acalculated 1.37 moles of C after all CO has been removed, and has 0%excess C.

Example 2

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together, at room temperature, 90%methyl terminated phenylethyl polysiloxane. (having 27% X) and 10% TV.This precursor formulation has 1.05 moles of hydride, 0.38 moles ofvinyl, 0.26 moles of phenyl, and 1.17 moles of methyl. The precursorformulation has the following molar amounts of Si, C and O based upon100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.17 20% C 3.47 60% O 1.17 20%

As calculated, the SiOC derived from this formulation will have acalculated 2.31 moles of C after all CO has been removed, and has 98%excess C.

Example 3

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 70%methyl terminated phenylethyl polysiloxane (having 14% X) and 30% TV.This precursor formulation has 0.93 moles of hydride, 0.48 moles ofvinyl, 0.13 moles of phenyl, and 1.28 moles of methyl. The precursorformulation has the following molar amounts of Si, C and O based upon100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.28 23% C 3.05 54% O 1.28 23%

As calculated, the SiOC derived from this formulation will have acalculated 1.77 moles of C after all CO has been removed, and has 38%excess C.

Example 4

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 50%methyl terminated phenylethyl polysiloxane (having 20% X) and 50% TV.This precursor formulation has 0.67 moles of hydride, 0.68 moles ofvinyl, 0.10 moles of phenyl, and 1.25 moles of methyl. The precursorformulation has the following molar amounts of Si, C and O based upon100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.25 22% C 3.18 56% O 1.25 22%

As calculated, the SiOC derived from this formulation will have acalculated 1.93 moles of C after all CO has been removed, and has 55%excess C.

Example 5

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 65%methyl terminated phenylethyl polysiloxane (having 40% X) and 35% TV.This precursor formulation has 0.65 moles of hydride, 0.66 moles ofvinyl, 0.25 moles of phenyl, and 1.06 moles of methyl. The precursorformulation has the following molar amounts of Si, C and O based upon100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.06 18% C 3.87 54% O 1.06 28%

As calculated, the SiOC derived from this formulation will have acalculated 2.81 moles of C after all CO has been removed, and has 166%excess C.

Example 6

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 65% MHFand 35% dicyclopentadiene (DCPD). This precursor formulation has 1.08moles of hydride, 0.53 moles of vinyl, 0.0 moles of phenyl, and 1.08moles of methyl. The precursor formulation has the following molaramounts of Si, C and O based upon 100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.08 18% C 3.73 64% O 1.08 18%

As calculated, the SiOC derived from this formulation will have acalculated 2.65 moles of C after all CO has been removed, and has 144%excess C.

Example 7

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 82% MHFand 18% dicyclopentadiene (DCPD). This precursor formulation has 1.37moles of hydride, 0.27 moles of vinyl, 0.0 moles of phenyl, and 1.37moles of methyl. The precursor formulation has the following molaramounts of Si, C and O based upon 100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.37 25% C 2.73 50% O 1.37 25%

As calculated, the SiOC derived from this formulation will have acalculated 1.37 moles of C after all CO has been removed, and has 0%excess C.

Example 8

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 46% MHF,34% TV and 20% VT. This precursor formulation has 0.77 moles of hydride,0.40 moles of vinyl, 0.0 moles of phenyl, and 1.43 moles of methyl. Theprecursor formulation has the following molar amounts of Si, C and Obased upon 100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.43 30% C 1.95 40% O 1.43 30%

As calculated, the SiOC derived from this formulation will have acalculated 0.53 moles of C after all CO has been removed, and has a 63%C deficit, or is 63% C starved.

Example 9

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 70% MHF,20% TV and 10% VT. This precursor formulation has 1.17 moles of hydride,0.23 moles of vinyl, 0.0 moles of phenyl, and 1.53 moles of methyl. Theprecursor formulation has the following molar amounts of Si, C and Obased upon 100 g of formulation.

Molar Ratio of Si, C, O (% of total Moles moles in “Moles” Column) Si1.53 31% C 1.87 38% O 1.53 31%

As calculated, the SiOC derived from this formulation will have acalculated 0.33 moles of C after all CO has been removed, and has a 78%C deficit, or is 78% C starved.

Example 10

A polysilocarb formulation using the mixing type method is formulated.The formulation is made by mixing together at room temperature 95% MHFAND 5% TV.

Example 11

Turning to FIG. 11 there is shown a schematic cross sectionalrepresentation of an apparatus for growing SiC crystals and crystallinestructures. The vapor deposition device 1700 has a vessel 1701 that isassociated with, (e.g., thermally associated, positioned to deliverelectromagnetic energy, has wrapped around it) various heating elements,e.g., 1702. The heating elements are configured and operated to provideat least two different temperature zones, Zone A, 1702 a, and Zone B,1702 b. Inside of the vessel 1701 there is a polymer derived ceramic1703, which is a source of Si and C. Additionally, inside the vessel1701 is a crystal grown initiation article 1704.

Thus, in general the polymer derived ceramic 703 is heated to atemperature in Zone A 1702 a to cause the SiC to sublimate, generally atemperature greater than about 2,000° C. The Si C vapors then rise intotemperature Zone B, which is cooler than Zone A. The Si C vapors aredeposited on the initiation article 704 as SiC.

It being understood that the schematic of the device 1700, is a teachingillustration, greatly simplified, and that commercial and industrialdevices can have additional components, such as control systems,monitors, gas handling and other devices and can also have differentconfigurations, presently known to those of skill in the art, as wellas, new devices and configurations that may be based, in part, upon theteachings of this specification.

Example 11a

In the vapor deposition device 1701 the polymer derived ceramic 1703 ishigh purity SiOC. The temperature of Zone A is gradually increased andheld at set temperatures to transition the SiOC to SiC and then to causethe SiC to sublimate and form an SiC crystal on the initiation article1704.

Example 11b

In this example the initiation article 1704 is a seed crystal and theSiC that is deposited from the polymer derived SiC in Zone A form analpha mono-crystalline boule. This boule is then sectioned to formpolysilocarb derived SiC wafers.

Example 11c

In this example the initiation article 1704 is a Si substrate and theSiC from the polymer derived SiC in Zone A is deposited on the substrateas an epitaxial polysilocarb derived SiC layer on the Si substrate.

Example 11d

In the vapor deposition device 1701 the polymer derived ceramic 703 ishigh purity SiOC, having 6 nines purity. The temperature of Zone A isgradually increased and held at set temperatures to transition the SiOCto SiC and then to cause the SiC to sublimate and form an SiC crystal onthe initiation article 1704.

Example 11e

In the vapor deposition device 1701 the polymer derived ceramic 703 ishigh purity SiOC, having less than 20 ppm Al. The temperature of Zone Ais gradually increased and held at set temperatures to transition theSiOC to SiC and then to cause the SiC to sublimate and form an SiCcrystal on the initiation article 1704.

Example 11f

In the vapor deposition device 1701 the polymer derived ceramic 1703 ishigh purity polysilocarb derived SiC, having less than 20 ppm Al. TheSiC sublimates to form a SiC crystal on the initiation article 1704,which is a seed crystal.

Example 12

The vapor deposition device 1701 is a hot wall reactor.

Example 13

The vapor deposition device 1701 is a multiwafer reactor.

Example 14

The vapor deposition device 1701 is a chimney reactor.

Example 15

A boule of polysilocarb derived SiC having a length of about 1 inch anda diameter of about 4 inches. The boule is alpha type and is free frommicropipes. The boule having less than 100, less than 10, and preferableno 1 micropores.

Example 15a

A boule of polysilocarb derived SiC has micropipe density of <10/cm²,<5/cm², <1/cm², <0.5/cm² and most preferably <0.1/cm².

Example 16

A metal-semiconductor filed effect transistor (MESFET) is made frompolysilocarb derived SiC. This MESFET is incorporated into compoundsemiconductor device, operating in the 45 GHz frequency range.

Example 17

A metal-semiconductor filed effect transistor (MESFET) is made frompolysilocarb derived SiC. This MESFET is incorporated into a componentof a cellular base station.

Example 18

A boule of polysilocarb derived SiC having a length of about 2 inchesand a diameter of about 4 inches. The boule is doped to form p wafersfor a semiconductor device.

Example 19

A boule of polysilocarb derived SiC having a length of about 2 inchesand a diameter of about 4 inches. The boule is doped to form n wafersfor a semiconductor device.

Example 20

Turning to FIG. 12 there is shown a schematic cross sectionalrepresentation of an apparatus for growing SiC crystals and crystallinestructures. The vapor deposition device 1800 has a vessel 1801 that isassociated with heat sources 1802. The heat sources, and vessel and heatsources, can be any of the assemblies described in this specification orthat are know to the art. The heat sources are configured and operatedto provide at least two different temperature zones, Zone A, 1802 a, andZone B, 1802 b. Inside of the vessel 1801 there is a polymer derivedceramic 1803, which is a source of Si and C. The polymer derived ceramic1803 is the polysilocarb of Example 6 that has been cured andtransformed into SiC according to Example 14. Additionally, inside thevessel 1801 is a crystal grown initiation article 1804.

Thus, in general the polymer derived ceramic 803 is heated to atemperature in Zone A 1802 a to cause the SiC to sublimate, generally atemperature greater than about 2,400° C. The Si C vapors then rise intotemperature Zone B, which is cooler than Zone A. The Si C vapors aredeposited on the initiation article 1804 as SiC.

It being understood that the schematic of the device 1800, is a teachingillustration, greatly simplified, and that commercial and industrialdevices can have additional components, such as control systems,monitors, gas handling and other devices and can also have differentconfigurations, presently known to those of skill in the art, as wellas, new devices and configurations that may be based, in part, upon theteachings of this specification.

Example 21

Turning to FIG. 13 there is shown a schematic cross sectionalrepresentation of an apparatus for growing SiC crystals and crystallinestructures. The vapor deposition device 1900 has a vessel 1901 that isassociated with heat sources 1902. The heat sources, and vessel and heatsources, can be any of the assemblies described in this specification orthat are know to the art. The heat sources are configured and operatedto provide at least two different temperature zones, Zone A, 1902 a, andZone B, 1902 b. Inside of the vessel 1901 there is a polymer derivedceramic 903, which is a source of Si and C. The polymer derived ceramic1903 is the polysilocarb of Example 7 that has been cured andtransformed into SiC according to Example 15. Additionally, inside thevessel 1901 is a crystal grown initiation article 1904.

Thus, in general the polymer derived ceramic 1903 is heated to atemperature in Zone A 1902 a to cause the SiC to sublimate, generally atemperature about 2,500° C. The Si C vapors then rise into temperatureZone B, which is cooler than Zone A. The Si C vapors are deposited onthe initiation article 1904 as SiC.

It being understood that the schematic of the device 1900, is a teachingillustration, greatly simplified, and that commercial and industrialdevices can have additional components, such as control systems,monitors, gas handling and other devices and can also have differentconfigurations, presently known to those of skill in the art, as wellas, new devices and configurations that may be based, in part, upon theteachings of this specification.

Example 22

Ultra pure SiOC, of the formulations provided in this specification andhaving at least about 5-nines, and preferably about 6-nines purity, isused to make transparent SiOC articles in the processes disclosed andtaught in U.S. Pat. No. 5,180,694, the entire disclosure of which isincorporated herein by reference.

Example 23

Ultra pure SiOC, of the formulations provided in this specification andhaving at least about 5-nines, and preferably about 6-nines purity isused to make SiOC layers and coatings on articles and in the processesdisclosed and taught in U.S. Pat. No. 8,981,564, the entire disclosureof which is incorporated herein by reference.

Example 24

Ultra pure SiOC, of the formulations provided in this specification andhaving at least about 5-nines, and preferably about 6-nines purity isused to make SiOC layers and coatings on articles and in the processesdisclosed and taught in U.S. Pat. No. 8,778,814, the entire disclosureof which is incorporated herein by reference.

Example 25

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, source material, growthmaterial, deposition material or raw material, in the apparatus andprocesses taught and disclosed in US Patent Application Publication No.2013/0255568 the entire disclosure of which is incorporated herein byreference.

A method for manufacturing silicon carbide single crystal having adiameter larger than 100 mm by sublimation includes the following steps.A seed substrate made of silicon carbide and silicon carbide rawmaterial are prepared. Silicon carbide single crystal is grown on thegrowth face of the seed substrate by sublimating the silicon carbide rawmaterial. In the step of growing silicon carbide single crystal, themaximum growing rate of the silicon carbide single crystal growing onthe growth face of the seed substrate is greater than the maximumgrowing rate of the silicon carbide crystal growing on the surface ofthe silicon carbide raw material. Thus, there can be provided a methodfor manufacturing silicon carbide single crystal allowing a thicksilicon carbide single crystal film to be obtained, when silicon carbidesingle crystal having a diameter larger than 100 mm is grown.

A method for manufacturing silicon carbide crystal of the presentembodiment is directed to manufacturing silicon carbide single crystalhaving a diameter larger than 100 mm by sublimation. The method includesthe following steps. A seed substrate made of silicon carbide andsilicon carbide raw material are prepared. Silicon carbide singlecrystal is grown on the growth face of the seed substrate by sublimatingthe silicon carbide raw material. In the step of growing silicon carbidesingle crystal, the maximum growing rate of the silicon carbide singlecrystal growing on the growth face of the seed substrate is greater thanthe maximum growing rate of the silicon carbide crystal growing on thesurface of the silicon carbide raw material.

Referring to FIG. 1 , the seed substrate and silicon carbide rawmaterial preparation step is carried out. Specifically, silicon carbideraw material 7 is placed in a crucible 20. A seed substrate 3 isarranged at a position facing silicon carbide raw material 7. Seedsubstrate 3 is held by a seed substrate holder 4. Seed substrate 3 ismade of silicon carbide single crystal. A growth face 6 of seedsubstrate 3 is the plane, for example. Growth face 6 may be a planeinclined by an off angle within approximately 8°, for example, relativeto the plane. Since the present embodiment corresponds to a method formanufacturing silicon carbide single crystal having a diameter largerthan 100 mm, the diameter of seed substrate 3 is also larger than 100mm.

Preferably in the step of growing silicon carbide single crystal, themaximum height of the silicon carbide single crystal growing on the seedsubstrate exceeds 20 mm. More preferably, the maximum height of thesilicon carbide single crystal growing on the seed substrate exceeds 50mm. Referring to FIG. 2 , a further embodiment of the embodiment of FIG.1 of a manufacturing device for silicon carbide single crystal accordingto the present embodiment will be described.

A manufacturing device 10 for silicon carbide single crystal accordingto the present embodiment is directed to growing silicon carbide singlecrystal having a diameter larger than 100 mm by sublimation.Manufacturing device 10 mainly includes a crucible 20, a heater 2, and ahollow member 5.

Crucible 20 is made of carbon. Silicon carbide raw material 7 is placedin crucible 20. Seed substrate 3 is arranged at a position facingsurface 8 of silicon carbide raw material 7. Seed substrate 3 is held bya seed substrate holder 4. Seed substrate holder 4 is held by a lidsection 12 of crucible 20.

Around a sidewall 13 of crucible 20 is provided a heater 2 to heatsilicon carbide raw material 7 placed in crucible 20. Heater 2 isarranged so as to also cover a bottom 11 of crucible 20. Preferably,heater 2 is arranged to cover the entire bottom 11 of crucible 20.Heater 2 may be an induction heating type heater, or a resistanceheating type heater.

Hollow member 5 is empty inside. Hollow member 5 is provided to extendtowards seed substrate 3 from bottom 11 of crucible 20 at the upper endface around the central region. Hollow member 5 is enclosed by siliconcarbide raw material 7. Preferably, hollow member 5 is embedded insilicon carbide raw material 7. The height of hollow member 5 is lowerthan the height of silicon carbide raw material 7. Furthermore, heater 2is located below hollow member 5. Since hollow member 5 is empty, thesurface of silicon carbide raw material 7 around the central region canbe heated efficiently by radiation. Thus, the temperature distributionof silicon carbide raw material 7 can be reduced. Alternatively,crucible 20 may have a bottom shaped protruding towards seed substrate 3around the central region, instead of providing hollow member 5.

The thickness of bottom 11 of crucible 20 is preferably greater than 10mm. More preferably, the thickness of bottom 11 of crucible 20 isgreater than or equal to 20 mm. Accordingly, bottom 11 of crucible 20can be heated efficiently by thermal conduction through carbon havingthermal conductivity higher than that of silicon carbide. Then, thesilicon carbide single crystal growing step is carried out.Specifically, by heating silicon carbide raw material 7 placed incrucible 20, silicon carbide raw material 7 is sublimated. Thesublimated raw material gas recrystallizes on growth face 6 of seedsubstrate 3, whereby silicon carbide single crystal is grown on growthface 6.

If the size of silicon carbide single crystal to be grown becomeslarger, the inner diameter of crucible 20 used must also be increased.If the inner diameter of crucible 20 is made larger, the distance fromheater 2 arranged at the outer side of crucible 20 to the center “b” atsurface 8 of silicon carbide raw material 7 (in other words, to theregion of surface 8 of silicon carbide raw material 7 facing the center“a” of seed substrate 3) becomes longer. Therefore, the temperaturedistribution of silicon carbide raw material 7 will become greater sincethe region around the center “b” at surface 8 of silicon carbide rawmaterial 7 is not readily heated.

If the temperature around the center “b” at surface 8 of silicon carbideraw material 7 becomes relatively low, the sublimated silicon carbidegas will be recrystallized on surface 8 of silicon carbide raw material7. Therefore, silicon carbide crystal will also grow on surface 8 ofsilicon carbide raw material 7. If silicon carbide crystal grows onsurface 8 of silicon carbide raw material 7, the space where siliconcarbide single crystal can grow on growth face 6 of seed substrate 3will become smaller, leading to difficulty in growing a thick siliconcarbide single crystal film.

According to the method for manufacturing silicon carbide single crystalof the present embodiment, the maximum growing rate of silicon carbidesingle crystal growing on growth face 6 of seed substrate 3 is greaterthan the maximum growing rate of silicon carbide crystal growing onsurface 8 of silicon carbide raw material 7. Therefore, when siliconcarbide single crystal having a diameter larger than 100 mm is grown, athick silicon carbide single crystal film can be obtained. Furthermore,the growing rate of silicon carbide single crystal growing on seedsubstrate 3 can be improved. Moreover, since growth of silicon carbidecrystal on surface 8 of silicon carbide raw material 7 can besuppressed, the change in the growing environment of silicon carbidesingle crystal on seed substrate 3 can be reduced. Accordingly,occurrence of crystal defect at the silicon carbide single crystal canbe reduced.

According to the method for manufacturing silicon carbide single crystalof the present embodiment, sublimation of silicon carbide raw materialin the step of growing silicon carbide single crystal is carried out byheating surface 8 of silicon carbide raw material 7 at a region facingthe center of seed substrate 3 through radiation. Accordingly, thetemperature distribution of silicon carbide raw material 7 can bereduced. As a result, a thick silicon carbide single crystal film can begrown on seed substrate 3 by suppressing the growth of silicon carbidecrystal on silicon carbide raw material 7.

The method for manufacturing silicon carbide single crystal of thepresent embodiment is carried out by heating the silicon carbide rawmaterial through hollow member 5. Accordingly, surface 8 of siliconcarbide raw material 7 around the central region can be heated moreefficiently by radiation, allowing the temperature distribution ofsilicon carbide raw material 7 to be reduced. As a result, a thicksilicon carbide single crystal film can be grown on seed substrate 3 bysuppressing growth of silicon carbide crystal on silicon carbide rawmaterial 7.

Example 26

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 8,216,369, theentire disclosure of which is incorporated herein by reference.

Unique electronic properties of silicon carbide (SiC) make it a verydesirable material for state-of-the-art semiconductor devices that canoperate at high frequencies, high voltages and current densities, and inharsh conditions. In many such devices, silicon carbide is utilized as asubstrate on which the semiconductor device structure is formed usingepitaxy, photolithography and metallization. Depending on the devicedesign, the substrate must possess specified electronic parameters, suchas conductivity type and resistivity. While devices operating at highand microwave frequencies (RF devices) require semi-insulating (SI)substrates with very high resistivity, for other devices, such as highpower switching devices, low-resistivity n-type and p-type substratesare needed.

Presently, SiC single crystals are grown on the industrial scale by asublimation technique called Physical Vapor Transport (PVT). A schematicdiagram of a typical prior art PVT arrangement is shown in FIG. 3 . InPVT, polycrystalline grains of silicon carbide (SiC source) 31 areloaded on the bottom of a growth container 32 and a SiC seed crystal 34is attached to a top of growth container 32. Desirably, growth container32 is made of a material, such as graphite, that is not reactive withSiC or any dopant (discussed hereinafter) added thereto. The loadedgrowth container 32 is evacuated, filled with inert gas to a certain,desired pressure and heated via at least one heating element 33 (e.g.,an RF coil) to a growth temperature, e.g., between 1900° C. and 2400° C.Growth container 32 is heated in such a fashion that a verticaltemperature gradient is created making the SiC source 31 temperaturehigher than that of the SiC seed 34. At high temperatures, siliconcarbide of the SiC source 31 sublimes releasing a spectrum of volatilemolecular species to the vapor phase. The most abundant of these gaseousspecies are Si, Si₂C and SiC₂. Driven by the temperature gradient, theyare transported to the SiC seed 34 and condense on it causing growth ofa SiC single crystal 35 on the SiC seed 34. Prior art patents in thisarea include, for example, U.S. Pat. Nos. 6,805,745; 5,683,507;5,611,955; 5,667,587; 5,746,827; and Re. 34,861, which are allincorporated herein by reference.

Those skilled in the art of semiconductor materials know that productionof SiC substrates with desirable electronic properties is impossiblewithout purposeful introduction of certain impurities in a process knownas doping. In silicon carbide, the chemical bonds are so exceptionallystrong and solid-state diffusion of impurities is so slow that doping inthe bulk can be accomplished only at the stage of crystal growth, whenthe doping element (dopant) incorporates directly into the lattice ofthe growing SiC crystal 35.

As a particular example of SiC doping during growth, n-type SiC crystalsare produced by adding small amounts of gaseous nitrogen (N₂) to growthcontainer 32 atmosphere. Nitrogen-doped SiC single crystals with veryuniform electrical properties can be readily grown by maintainingappropriate partial pressure of N₂ during growth.

With the exception of the nitrogen-doped crystals, attaining uniformelectrical properties in other types of SiC crystals, includingsemi-insulating, p-type and phosphorus doped n-type crystals, is muchmore difficult because the doping compounds are not gaseous but solid.Vanadium is one particularly important dopant, which is used to producea high-resistivity semi-insulating SiC crystal. Aluminum is anotherimportant dopant used for the growth of conductive crystals of p-type.Other solid dopants include boron, phosphorus, heavy metals and rareearth elements.

Prior art doping of SiC crystals using a solid dopant is carried out byadmixing small amounts of impurity directly to the SiC source 31. Forinstance, vanadium can be introduced in the form of elemental vanadium,vanadium carbide or vanadium silicide. Aluminum can be introduced in theelemental form, aluminum carbide or aluminum silicide. Other suitablesolid dopants, such as boron or phosphorus, can be similarly introducedas elements, carbides or silicides. The doping compound can be in thephysical form of powder, pieces or chips.

During SiC crystal 35 sublimation growth, multi-step chemical reactionstake place between the SiC source 31 and the dopant admixed directly inthe SiC source. These reactions proceed through several stages and leadto the formation of multiple intermediary compounds. In the case ofvanadium doping, thermodynamic analysis shows that the product ofreaction between SiC and vanadium dopant (whether elemental, carbide orsilicide) depends on the stoichiometry of SiC. That is, when the SiCsource 31 is Si-rich and its composition corresponds to the two-phaseequilibrium between SiC and Si, formation of vanadium silicide (VSi₂) islikely. When the SiC source is C-rich and its composition corresponds tothe two-phase equilibrium between SiC and C, formation of vanadiumcarbide (VC_(x)) is likely.

It is known that freshly synthesized SiC source 31 is, typically,Si-rich. Due to the incongruent character of SiC sublimation, theinitially silicon-rich SiC source 31 gradually becomes carbon-rich. Thischange in the stoichiometry of the SiC source 1 during sublimationgrowth causes the following sequence of reactions:

During initial stages of growth, when the SiC source 31 is Si-rich,reaction between vanadium dopant and SiC yields vanadium silicide VSi₂.

As the growth progresses and the SiC source 31 becomes more carbon-rich,vanadium silicide converts to intermediate carbo-silicide VC_(x)Si_(y).

During final stages of growth, when the SiC source 31 is carbon-rich,vanadium carbo-silicide converts into vanadium carbide VC.

A physical vapor transport system includes a growth chamber charged withsource material and a seed crystal in spaced relation, and at least onecapsule having at least one capillary extending between an interiorthereof and an exterior thereof, wherein the interior of the capsule ischarged with a dopant. Each capsule is installed in the growth chamber.Through a growth reaction carried out in the growth chamber followinginstallation of each capsule therein, a crystal is formed on the seedcrystal using the source material, wherein the formed crystal is dopedwith the dopant.

With reference to FIG. 4 , the advantages of spatially uniform andcontrolled doping are realized using a time-release capsule 44, which isloaded with a stable form of solid dopant, and placed inside growthcontainer 32 (of FIG. 3 ). Capsule 44 is desirably made of an inertmaterial, which is reactive with neither SiC nor the dopant. For amajority of applications, dense and low-porosity graphite is a preferredmaterial for capsule 44. Other possible materials include refractorymetals, their carbides and nitrides. However, this is not to beconstrued as limiting the embodiment.

Capsule 44 includes a tight lid 45 having one or more calibratedthrough-holes or capillaries 46 of predetermined diameter and length.There are no limitations on the dimensions of capsule 44 except that itshould fit inside growth container 32 and not restrict the flow of vaporto the SiC seed 34.

At a suitable time, capsule 44 is loaded with the proper amount of soliddopant 47. Dopant 47 must be either in a stable chemical form that isnot reactive with the material of capsule 44 or in a form that uponreaction with the material forming capsule 44 produces a stablecompound. For the majority of practical applications, the preferredforms of solid dopant are: (i) elemental form, (ii) carbide and (iii)silicide. However, this is not to be construed as limiting theembodiment.

During sublimation growth of the SiC crystal 35, capsule 44 is situatedinside growth container 32.

In one embodiment, shown in FIG. 5 a , a single capsule 54 is positionedon the top surface of the SiC source near the axis of growth container52. In another embodiment, shown in FIG. 5 b , several capsules 54 arepositioned on the top surface of the SiC source near the wall of growthcontainer 52. In yet another embodiment, shown in FIG. 5 c , capsule 54is buried within the material forming the SiC source.

The principle of operation of capsule 54 is based on the well-knownphenomenon of effusion, i.e., the slow escape of vapor from a sealedvessel through a small orifice. At high temperatures, the vapor pressureof dopant inside capsule forces it to escape through each capillary. Ifthe cross section of each capillary is sufficiently small, the vaporpressure of dopant in capsule does not differ substantially from theequilibrium value.

The laws of effusion are well-known and, forgiven growth conditions(temperature, vapor pressure of the inert gas, volatility of thesubstance contained in capsule 54, capillary diameter and capillarylength), the flux of the molecules of dopant escaping capsule 54 viaeach capillary can be readily calculated. Thus, the dimension of eachcapillary and number of capillaries can be tailored to achieve a steadyand well-controlled flux of the impurity dopant atoms from capsule 54 tothe growing SiC crystal.

For relatively small doping levels, a capsule 54 having a singlecapillary can be used (see embodiment in FIG. 5 a ). For higher dopinglevels or doping with multiple dopants, multiple capsules 54 can be used(see embodiment in FIG. 5 b ), as well as a capsule 54 with multiplecapillaries. For special purposes, such as programmable or delayeddoping, one or more time-release capsules 54 buried in the depth of theSiC source can be utilized (see embodiment in FIG. 5 c ).

According to prior art SiC doping, a small amount of dopant is admixeddirectly to the SiC source material, leading to chemical reactionsbetween the dopant and SiC source. These reactions, combined withchanges in the stoichiometry of the SiC source material, lead toprogressive changes in the partial pressure of the dopant. As a result,prior art doping produces initially high concentrations of dopant in thecrystal followed by a decrease in the dopant concentration over the SiCcrystal length. Crystals grown according to the prior art have too higha degree of dopant in the first-to-grow sections and insufficient dopantin the last-to-grow sections. The dopant level in the first-to-growboule sections can be so high that second-phase precipitates form in thecrystal bulk leading to the generation of crystal defects.

The present embodiment eliminates the problems of the prior art by usingone or more time-release capsules for the doping of SiC crystals duringcrystal growth. The embodiment has two distinct advantages:

First, the present embodiment eliminates direct contact between thedopant and the SiC source. This is accomplished by placing the dopantinside of a capsule made of an inert material.

Second, the present embodiment offers a means for precise control of thedopant concentration. This is achieved by choosing the number ofcapsules, the number and dimensions of the capillaries, and the positionof each capsule within growth container.

The present embodiment offers the following technical advantages overthe prior art. First, it eliminates direct contact between the dopantand the SiC source, so the transient processes associated with thechemical reactions between the dopant and SiC source are avoided oreliminated. Secondly, the present embodiment provides a means toprecisely control the flux of the dopant to the SiC seed. Thesetechnical advantages lead to the production of precisely and uniformlydoped SiC crystals.

The direct consequence of precise and spatially uniform doping is SiCsingle crystals with spatially uniform and controllable electricalproperties. In addition to the superior electrical properties, theembodiment avoids or eliminates the formation of impurity precipitatesand associated defects and, thus, leads to the improvement in the SiCcrystal quality and wafer yield.

Specifically, for a vanadium doped SiC crystal, the application of thepresent embodiment increases the yield of usable prime quality SiCwafers by as much as 50%. This in-turn leads to reduced costs andimproved profitability.

The present embodiment can be applied to the growth of semi-insulating6H—SiC single crystals doped during growth with vanadium. However, thisis not to be construed as limiting the embodiment since it is envisionedthat the embodiment can also be applied to the growth of 4H—SiC, 3C—SiCor 15R-SiC single crystals doped during growth with a suitable dopant.In Examples 2 and 3 below, a single time-release capsule made of puredense graphite is used. All other parameters of the SiC growth process,such as temperature, pressure, temperature gradient, etc., are inaccordance with existing growth techniques used for the production ofSiC crystals.

Example 27

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 8,512,471 the entiredisclosure of which is incorporated herein by reference. The ultra pureSiC materials greatly improve the process and apparatus of the U.S. Pat.No. 8,512,471 patent, by enhancing or potentially eliminating, e.g.,making unnecessary, the need for that patent's methods and apparatus toremove Boron and other impurities.

In a physical vapor transport growth technique for silicon carbide asilicon carbide powder and a silicon carbide seed crystal are introducedinto a physical vapor transport growth system and halosilane gas isintroduced separately into the system. The source powder, the halosilanegas, and the seed crystal are heated in a manner that encouragesphysical vapor transport growth of silicon carbide on the seed crystal,as well as chemical transformations in the gas phase leading toreactions between halogen and chemical elements present in the growthsystem.

Physical Vapor Transport (PVT) is the most common sublimation techniqueused for SiC crystal growth. A schematic diagram of the conventional PVTarrangement is shown in FIG. 6 . Generally, growth is carried out in agraphite crucible 61 sealed with a graphite lid 62 and loaded with asublimation source 63 and a seed 64. Generally, a polycrystalline SiCsource 63 is disposed at the bottom of the crucible 61 and a SiC seed 64at the top of crucible 61. The seed 64 is often mounted directly to thecrucible lid 62 using adhesives or other suitable means. Crucible 61 isheated to a growth temperature, generally between 2000° C. and 2400° C.,where source 63 vaporizes and fills crucible 61 with volatile molecularspecies of Si₂C, SiC₂ and Si. During growth, the temperature of source63 is maintained higher than the temperature of the seed 46. Thistemperature difference forces the vapors from source 63 to migrate andprecipitate on seed 64 forming a single crystal 65. In order to controlthe growth rate and ensure high crystal quality, PVT growth is carriedout under a small pressure of inert gas, generally between several and200 Torr.

It is known that the permeability of graphite depends on the nature ofthe gas diffusing through graphite. Graphite is generally permeable toinert gases, hydrogen and nitrogen, but has a much lower permeability tothe elements that form stable carbides. Accordingly, graphite has a verylow permeability to the vapors formed during sublimation of siliconcarbide, such as Si, Si₂C and SiC₂. Therefore, conventional PVT can beviewed as a “closed” process, in which the Si-bearing vapors practicallydo not leave the growth crucible, except small unintentional losses thatcan occur through the joint between the crucible body 61 and lid 62.

SiC single crystals have also been grown using “open” processes, where adeliberate gas flow is established between the crucible interior andexterior. Examples include High Temperature Chemical Vapor Deposition(HTCVD), Halide Chemical Vapor Deposition (HCVD) and some PVTmodifications. A generalized diagram of the open SiC growth process isshown in FIG. 7 . Similarly to the closed sublimation growth process,the open process is carried out in a graphite crucible 71, whereinsource 73 is disposed at the crucible bottom and seed 74 is disposed atthe crucible top. Graphite crucible 71 used in the open process isprovided with a gas inlet 7 and gas outlet(s) 79. A gas mixture 76, thatmay contain Si precursors, C precursors, dopants and other gaseouscomponents, enters the crucible through an inlet 77. Once inside thecrucible 71, the reactants undergo chemical transformations in areaction zone 78. The gaseous reaction products blend with the vaporsoriginating from solid source 73 and move toward seed 4, where theyprecipitate on seed 74 and form single crystal 75. Gaseous byproductsescape through gas outlet(s) 79. In the process of Halide Chemical VaporDeposition (HCVD), the silicon and carbon precursors are delivered tothe reaction zone 78 in the form of silicon tetrachloride (SiC₄) andpropane (C₃H₈) mixed with a large excess of hydrogen. The main drawbackof the open SiC sublimation growth process is related to severe lossesof Si-bearing vapors through the outlet port(s) 79.

Graphite is widely utilized in SiC sublimation growth as a material forcrucibles, seed-holders, heat shields and other parts. The startingmaterials used in graphite manufacturing (coke and pitch) contain boron.Therefore, boron is always present in graphite, where its atoms arechemically bound to carbon. High-temperature treatment under ahalogen-containing atmosphere is widely used by graphite manufacturersfor purification. During purification, the halogen molecules penetratethe graphite bulk, react with various impurities and form volatilehalides with them. Driven by the concentration gradient, the halidemolecules diffuse from the graphite bulk toward the surface, where theyare removed by the flow of the carrier gas. Typically, removal ofmetallic impurities from graphite is more efficient than removal ofboron.

Conventionally, graphite manufacturers characterize graphite purity bythe “ash content”, i.e., the amount of ash that remains after a graphitespecimen is burnt in oxygen. The best-purity commercially availablegraphite contains between 5 and 20 ppm of ash by weight. Boron formsvolatile oxide upon burning in oxygen; therefore, graphite manufacturersseldom specify boron content in graphite. Impurity analyses using GlowDischarge Mass Spectroscopy (GDMS) show that the boron content even inthe lowest-ash graphite is, typically, above 0.2 ppm and, in some cases,up to 1 ppm.

Furnaces used for graphite purification are, typically, very large andcapable of accommodating metric tons of graphite. Cross-contaminationbetween different items in a large graphite batch and contamination fromthe furnace itself limit the purification efficiency. As a result of theabove limitations, graphite with a boron content below 0.1 ppm by weightis not readily available on a regular commercial basis.

Optimization of conventional PVT sublimation growth, includingprotective coatings applied to interior surfaces of a graphite crucible,has led to the reduction of boron in the grown SiC crystals to(2-3)·10¹⁶ cm⁻³. However, in order to produce semi-insulating SiCcrystals of better quality and with superior electrical parameters, theconcentration of unintentional boron must be reduced to levels below10¹⁶ cm⁻³.

The strong reduction of unintentional boron in SiC crystals can beachieved if the growth process is combined with simultaneous removal ofboron from the growth crucible. It is believed that heretofore in-situpurification of SiC crystals during growth was not known in the art.

SiC sublimation growth utilizes crucibles, seed-holders, heat shieldsand other parts made of graphite. Generally, graphite containsdetectable levels of boron impurity, which can contaminate the growingcrystal. To overcome this problem, SiC sublimation growth is carried outin the presence of dynamic reactive atmosphere comprised of an inertcarrier gas and at least one reactive gas. The flow of reactive gas issupplied into the graphite growth crucible through an inlet port, and itescapes the crucible by filtering out across the permeable cruciblewall.

The main reactive component of the gas mixture is a halosilane gas,desirably tetrahalosilane, such as tetrachlorosilane (SiCl₄) ortetrafluorosilane (SiF₄). The halosilane additive is added inconcentrations between 0.1 and 10% by volume and, more desirably,between 1 and 5%. At high temperatures of SiC sublimation growth, thehalosilane undergoes pyrolysis forming lower halosilanes, such as SiCll₃and SiCl₂. The products of pyrolysis react with boron forming volatileboron halides, such as BCl, BCl₂ and BCl₃. The boron-containingbyproducts are removed from the interior of the growth crucible by theflow of the gas mixture, which passes across (thorough) the permeablecrucible wall.

Lower halosilanes can attack the SiC source and growing crystal, leadingto losses of silicon from the growth charge. In order to reduce theselosses, the gas mixture can include small amounts of hydrogen, desirablybetween 0.1 to 3% by volume. The presence of hydrogen shifts thethermodynamic equilibrium in the gas phase in such a fashion thatchemical attack on the SiC source and crystal is reduced.

The grown crystals are characterized by the concentration ofunintentional boron acceptor below 7·10¹⁵ cm⁻³ and resistivity above 10⁷Ohm·cm.

Disclosed herein is a crystal growth method that includes (a) providingan enclosed growth crucible inside of a growth chamber with a thermalinsulation disposed therebetween, the growth crucible havingpolycrystalline source material and a seed crystal disposed in spacedrelation therein; (b) heating the interior of the growth crucible suchthat a temperature gradient forms between the source material and theseed crystal, the source material is heated to a sublimation temperatureand the temperature gradient is sufficient to cause sublimated sourcematerial to be transported to the seed crystal where the sublimatedsource material precipitates on the seed crystal; and (c) causing a gasmixture to flow into the growth crucible and between the polycrystallinesource material and an interior surface of the growth crucible,whereupon the gas mixture reacts with an unwanted element in the body ofthe growth crucible to form a gaseous byproduct which flows through thegrowth crucible to the exterior of the growth crucible, which is formedof a material that is permeable to the gas mixture and the gaseousbyproduct, under the influence of the flow of the gas mixture into thegrowth crucible, wherein the unwanted element is boron and the gasmixture comprises the combination of (a) halosilane gas and (b) an inertgas.

The inert gas can be either argon or helium.

The halosilane gas can be tetrahalosilane in a concentration in the gasmixture between either 0.1% and 10% by volume, or between 1% and 5% byvolume.

The gas mixture can further include hydrogen. The concentration ofhydrogen in the gas mixture can be between 0.1% and 3% by volume.

The polycrystalline source material can be disposed in a source cruciblewhich is disposed inside the growth crucible in spaced relation tointerior surfaces of the growth crucible. An exterior of a base of thesource crucible can be disposed in spaced relation to an interior of afloor of the growth crucible, thereby defining a first gap therebetween.An exterior of a wall of the source crucible can be disposed in spacedrelation to an interior of a wall of the growth crucible, therebydefining a second gap therebetween.

The gas mixture can flow in the first and second gaps.

The flow of the gas mixture can be between 20 and 200 sccm.

The wall(s) of the growth crucible can have a thickness that is betweeneither 4 mm and 20 mm, or between 8 mm and 16 mm.

The growth crucible can be made from graphite. The growth chamber can bemade from fused silica. The thermal insulation can be made from a porousgraphite.

Also disclosed herein is a crystal growth method that comprises (a)providing a seed crystal and a source material in spaced relation insideof a growth crucible is made from a material that is at least in-partgas permeable and which includes an element in the body thereof that isnot wanted in a crystal grown in the growth crucible; (b) heating thegrowth chamber whereupon the source material sublimates and istransported via a temperature gradient in the growth chamber to the seedcrystal where the sublimated source material precipitates; and (c)concurrent with step (b), causing a gas mixture to flow inside thegrowth crucible in a manner whereupon the unwanted element reacts withthe gas mixture and is transported to the exterior of the growthcrucible via the at-least gas permeable part thereof.

The gas mixture can flow through the growth crucible at a rate between20 standard cubic centimeters per minute (seem) and 200 sccm.

The source material can be disposed in a source crucible that ispositioned inside the growth crucible. The exterior wall of the sourcecrucible can be spaced from an interior wall of the growth crucible. Thespace can be between 4 mm and 7 mm.

The unwanted element can be boron. The gas mixture can be a combinationof (a) halosilane gas and (b) an inert gas.

The growth crucible can be comprised of graphite. The source materialand the seed crystal can comprise SiC.

With reference to FIG. 8 , more specifically, PVT sublimation growth ofsilicon carbide is carried out in a graphite growth crucible 1 sealedwith a graphite lid 2. Desirably, crucible 81 and lid 82 are made ofhigh-density, fine-grain and low-porosity graphite, such as “ATJ”available from Union Carbide Corporation of Danbury, Conn., underregistered trademark UCAR® (registration number 1008278), or similar.Growth crucible 81 is loaded with a SiC polycrystalline source 3 and anoncrystalline seed crystal 84. Source 83 is disposed in a lower portionof the crucible 81 while seed 84 is disposed at the top of the crucible,desirably attached to crucible lid 82, as shown in FIG. 8 . Source 3 iscontained in a thin-walled graphite source crucible 83 a, which rests ona graphite pedestal 83 b. The dimensions of growth crucible 81, sourcecrucible 83 a and pedestal 83 b are such that a gap 810 exists betweenthe wall of the source crucible 83 a and the wall of the growth crucible81. Desirably, this gap is between 4 and 7 mm wide.

Growth crucible 1, loaded with source 83 and seed crystal 84, is placedinside a chamber 820 of the growth station, where it is surrounded by athermal insulation 812. Thermal insulation 812 is made of lightweightfibrous graphite, such as graphite felt or foam. The growth stationincludes a means for heating crucible 81 to a growth temperature. In oneparticular embodiment, the chamber 820 is water-cooled and is made offused silica, and the heating means is realized by an exterior RF coil823. Metal chambers with resistive heaters or RF coils located insidethe chamber can also or alternatively be utilized.

In order to initiate sublimation growth, crucible 81 is heated to thegrowth temperature, desirably between 2000° C. and 2400° C. At thegrowth temperature, SiC source 83 sublimes and fills the interior of thecrucible 81 with vapor including Si, Si₂C and SiC₂ volatile molecules.During growth, the temperature of source 83 is kept higher than thetemperature of seed crystal 84. This results in vapor transport in thedirection from source 83 to seed crystal 84. After reaching seed crystal84, the vapors condense thereon causing growth of a SiC single crystal85 on seed crystal 84.

During growth of single crystal 85, a gas mixture 86 is supplied intogrowth crucible 81 by passing first through an inlet 821 of chamber 820and then through an inlet port 87 of crucible 81. After entering growthcrucible 81, gas mixture 86 flows through windows W in pedestal 83 b andin the gap 810 formed between walls of growth crucible 1 and the sourcecrucible 83 a, as shown in FIG. 8 .

Gas mixture 86 supplied into growth crucible 81 is comprised of an inertcarrier gas, desirably argon or helium, and one or more reactive gaseousadditives. The main reactive additive is a halosilane gas, desirablytetrahalosilane (SiCl₄ or SiF₄). The concentration of halosilane in thegas mixture is desirably between 0.1 and 10% by volume, and moredesirably between 1 and 5%. The gas mixture may contain another reactivegaseous additive, such as hydrogen. The concentration of hydrogen isdesirably between 0.1 and 3% by volume.

Inside growth crucible 81, the halosilane gas reacts with boron andconverts it into volatile boron halides. These gaseous boron byproductsare removed from the interior of the crucible 81 by filtering throughthe permeable wall of the crucible 81. Thereafter, these byproducts areremoved from growth chamber 820 through an outlet port 822 by the flowof gas mixture 86 into growth chamber 820.

The chemical form of boron in the conditions of SiC sublimation growthis not exactly known. It is assumed that at high temperatures and in thepresence of carbon and SiC, boron can be either in the form of elementalboron vapor, or in the form of a chemical compound with carbon, or inthe form of a chemical compound with silicon. It is commonly believedthat boron contained in graphite bulk is chemically bound to carbon andforms chemical bonds similar to those of boron carbide, B₄C.

At the high temperatures of SiC sublimation growth, the halosilaneadditive undergoes pyrolysis. Pyrolysis of tetrahalosilane produceslower halosilanes. For example, the main products of SiCl₄ pyrolysis areSiCl₂ and SiCl₃. Thermodynamic analysis shows that, independently of thechemical form of boron, whether elementally or chemically bound tocarbon or silicon, the lower halosilanes would react withboron-containing molecules and produce volatile boron halides, such asBCI, BCl₂ and BCl₃.

Argon and helium, as well as gaseous boron halides, have sufficientpermeability in graphite. Therefore, efficient removal of gaseous boronbyproducts from growth crucible 81 can be realized by establishing theirflow across the permeable wall of crucible 81. This can be achievedusing the flow of carrier gas 86 across the crucible wall. In FIG. 8 ,arrows 811 symbolize the removal of boron halide products with the flowof carrier gas 6 passing across the crucible wall.

An additional benefit of the halosilane reactive additive is in itsability to react with boron contained in the bulk of graphite. Whilefiltering across the crucible wall, carrier gas 86 delivers the productsof halosilane pyrolysis into the graphite bulk, where they react withboron chemically bound to carbon. The flow of inert carrier gas 86across the crucible wall facilitates the removal of volatile boronhalides to the exterior of growth crucible 81.

At high temperatures, certain products of halosilane pyrolysis canattack SiC source 83 and growing crystal 85. For instance, higherhalosilane SiCl₃ can attack SiC leading to the appearance of free carbonand lower halosilane SiCl₂. This process can lead to removal of siliconfrom growth crucible 81, depletion of the SiC source 83 by silicon, anderosion of the SiC crystal 85. In order to avoid this, the gas mixturesupplied into crucible 81 contains a small amount of hydrogen. Thepresence of hydrogen in the gas phase leads to the appearance of smallquantities of hydrogen halides (HCl in the case of SiCl₄ and HF in thecase of SiF₄) and shifts the thermodynamic equilibrium in such a fashionthat chemical attack on the SiC source 83 and crystal 85 is greatlyreduced. In order to achieve this, the amount of hydrogen in the gasmixture is desirably between 0.1 to 3% by volume.

In order for boron removal to be effective, the flow of gas mixture 6 isdesirably between 20 sccm and 200 sccm. Too high of a flow can create aharmful overpressure inside crucible 81 and/or disturb the growthprocess, while too low of a flow can be ineffective or lead to theescape of Si-bearing vapors through the inlet port 87 of crucible 81.

The crucible wall should be thin enough to allow efficient escape of thevolatile boron halides by filtering/diffusion. At the same time, thecrucible wall must not be too thin, otherwise, it may become transparentto the silicon-bearing vapors such as SiC₂, Si₂C and Si and cause Silosses from the crystal growth source 83. Desirably, the thickness ofthe graphite crucible wall is desirably between 4 mm and 20 mm and, moredesirably, between 8 mm and 16 mm.

In summary, removal of boron from the growth crucible is carried outin-situ during SiC crystal growth. To this end, a reactive gas mixtureis supplied into the growth crucible through an inlet port, and itescapes the crucible by filtering out through the permeable cruciblewall. The gas mixture is comprised of an inert carrier gas and ahalosilane gas, desirably SiCl₄ or SiF₄, added in quantities between 0.1and 10% by volume, and more desirably between 1 and 5%. Even moredesirably, a small amount of hydrogen is added to the gas mixture inconcentrations between 0.1 and 3% by volume. At high temperatures, thehalosilane additive undergoes pyrolysis. The pyrolysis products reactwith boron, including boron residing in graphite. As a result ofreaction, volatile boron halides are produced. Subsequently, they areremoved from the growth crucible by filtering out across the permeablecrucible wall, assisted by the flow of carrier gas. The hydrogenadditive reduces the chemical attack of the SiC source and crystal andlosses of silicon from the growth crucible. The grown crystal 85 has aconcentration of unintentional boron acceptor below 7·10¹⁵ cm⁻³ andresistivity above 10⁷ Ohm·cm.

In summary, the foregoing description discloses, among other things:

A process for sublimation growth of SiC single crystals, in which growthis carried out under dynamic reactive atmosphere.

The use of a reactive atmosphere for SiC sublimation growth comprised ofan inert carrier gas, desirably, pure argon or helium, mixed withreactive gas additives.

The use of a reactive gas additive comprising a halosilane, desirablySiCl₄ or SiF₄.

The use of a reactive atmosphere for SiC sublimation growth, whichincludes a combination of halosilane and hydrogen.

The use of a reactive atmosphere for SiC sublimation growth, in whichthe concentration of halosilane is desirably between 0.1 and 10% byvolume, and more desirably between 1 and 5% by volume.

The use of a reactive atmosphere for SiC sublimation growth, in whichthe concentration of hydrogen is desirably between 0.1 and 3% by volume.

A process of PVT sublimation growth under a continuous flow of areactive gas mixture, in which the reactive gas mixture enters thegrowth crucible through an inlet port and escapes the crucible byfiltering across the permeable crucible wall.

A process of PVT sublimation growth under continuous flow of a reactivegas mixture, where the flow rate of the gas mixture is desirably between10 sccm and 200 sccm, and more desirably between 20 sccm and 100 sccm.

A growth crucible made of dense, fine-grain and low-porosity graphitehaving the wall desirably between 4 mm and 20 mm thick, and moredesirably between 8 mm and 16 mm thick.

A SiC sublimation growth process, in which the SiC source is containedin a thin-walled crucible disposed inside the growth crucible in such afashion that a gap exists between the base and wall of the growthcrucible and the base and wall of the source crucible. The gap betweenthe walls of the growth crucible and the source crucible is desirablybetween 2 mm and 10 mm wide, and more desirably between 4 mm and 7 mmwide.

SiC single crystals of 4H, 6H, 15R and 3C polytypes having unintentionalboron acceptor in concentrations below 7·10¹⁵ cm⁻³.

Technical advantages of the above-described method and apparatusinclude:

Reduced concentration of unintentional boron acceptors in 6H and 4H SiCcrystals;

Higher and spatially more uniform resistivity in semi-insulating SiCcrystals; and

Higher yield of semi-insulating substrates per boule.

Example 28

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in US Patent Application PublicationU.S. Pat. No. 6,824,611 the entire disclosure of which is incorporatedherein by reference.

A method and apparatus for controlled, extended and repeatable growth ofhigh quality silicon carbide boules of a desired polytype is disclosedwhich utilizes graphite crucibles coated with a thin coating of a metalcarbide and in particular carbides selected from the group consisting oftantalum carbide, hafnium carbide, niobium carbide, titanium carbide,zirconium carbide, tungsten carbide and vanadium carbide.

Silicon carbide is a perennial candidate for use as a semiconductormaterial. Silicon carbide has a wide bandgap, a low dielectric constant,and is stable at temperatures far higher than temperatures at whichother semiconductor materials, such as silicon, become unstable. Theseand other characteristics give silicon carbide excellent semiconductingproperties. Electronic devices made from silicon carbide can be expectedto perform, inter alia, at higher temperatures, faster speeds and athigher radiation densities, than devices made from other commonly usedsemiconductor materials such as silicon.

Those familiar with solid-state physics and the behavior ofsemiconductors know that a semiconductor material must have certaincharacteristics to be useful as a material from which electrical devicesmay be manufactured. In many applications, a single crystal is required,with low levels of defects in the crystal lattice, along with low levelsof unwanted chemical and physical impurities. If the impurities cannotbe controlled, the material is generally unsatisfactory for use inelectrical devices. Even in a pure material, a defective latticestructure can prevent the material from being useful.

Silicon carbide possesses other desirable physical characteristics inaddition to its electrical properties. It is very hard, possessing ahardness of 8.5-9.25 Mohs depending on the polytype [i.e., atomicarrangement] and crystallographic direction. In comparison, diamondpossesses a hardness of 10 Mohs. Silicon carbide is brilliant,possessing a refractive index of 2.5-2.71 depending on the polytype. Incomparison, diamond's refractive index is approximately 2.4.Furthermore, silicon carbide is a tough and extremely stable materialthat can be heated to more than 2000° C. in air without sufferingdamage. These physical characteristics make silicon carbide an idealsubstitute for naturally occurring gemstones. The use of silicon carbideas gemstones is described in U.S. Pat. Nos. 5,723,391 and 5,762,896 toHunter et al.

Accordingly, and because the physical characteristics and potential usesfor silicon carbide have been recognized for some time, a number ofresearchers have suggested a number of techniques for forming crystalsof silicon carbide. These techniques generally fall into two broadcategories, although it will be understood that some techniques are notnecessarily so easily classified. The first technique is known aschemical vapor deposition (CVD) in which reactants and gases areintroduced into a system within which they form silicon carbide crystalsupon an appropriate substrate.

The other main technique for growing silicon carbide crystals isgenerally referred to as the sublimation technique. As the designation“sublimation” implies, sublimation techniques generally use some kind ofsolid silicon carbide starting material, which is heated until the solidsilicon carbide sublimes. The vaporized silicon carbide startingmaterial is then encouraged to condense on a substrate, such as a seedcrystal, with the condensation intended to produce the desired crystalpolytype.

One of the first sublimation techniques of any practical usefulness forproducing better crystals was developed in the 1950s by J. A. Lely, andis described in U.S. Pat. No. 2,854,364. From a general standpoint,Lely's technique lines the interior of a carbon vessel with a siliconcarbide source material. By heating the vessel to a temperature at whichsilicon carbide sublimes, and then allowing it to condense,re-crystallized silicon carbide is encouraged to deposit along thelining of the vessel.

The Lely sublimation technique was modified and improved upon by severalresearchers. Hergenrother, U.S. Pat. No. 3,228,756 (“Hergenrother '756”)discusses another sublimation growth technique, which utilizes a seedcrystal of silicon carbide upon which other silicon carbide condenses togrow a crystal. Hergenrother '756 suggests that in order to promoteproper growth, the seed crystal must be heated to an appropriatetemperature, generally over 2000° C. in such a manner that the timeperiod during which the seed crystal is at temperatures between 1800° C.and 2000° C. is minimized.

Ozarow, U.S. Pat. No. 3,236,780 (“Ozarow '780”) discusses anotherunseeded sublimation technique which utilizes a lining of siliconcarbide within a carbon vessel. Ozarow '780 attempts to establish aradial temperature gradient between the silicon carbide lined innerportion of the vessel and the outer portion of the vessel.

Knippenberg, U.S. Pat. No. 3,615,930 (“Knippenberg '930”) and U.S. Pat.No. 3,962,406 (“Knippenberg '406”) discuss alternative methods forgrowing silicon carbide in a desired fashion. The Knippenberg '930patent discusses a method of growing p-n junctions in silicon carbide asa crystal grows by sublimation. According to the discussion in thispatent, silicon carbide is heated in an enclosed space in the presenceof an inert gas containing a donor type dopant atom. The dopant materialis then evacuated from the vessel and the vessel is reheated in thepresence of an acceptor dopant. This technique is intended to result inadjacent crystal portions having opposite conductivity types therebyforming a p-n junction.

The Knippenberg '406 patent discusses a three-step process for formingsilicon carbide in which a silicon dioxide core is packed entirelywithin a surrounding mass of either granular silicon carbide ormaterials that will form silicon carbide. The packed mass of siliconcarbide and silicon dioxide is then heated. The system is heated to atemperature at which a silicon carbide shell forms around the silicondioxide core, and then further heated to vaporize the silicon dioxidefrom within the silicon carbide shell. Finally, the system is heatedeven further to encourage additional silicon carbide to continue to growwithin the silicon carbide shell.

Vodakov, U.S. Pat. No. 4,147,572 discusses a geometry orientedsublimation technique in which solid silicon carbide source material andseed crystals are arranged in a parallel close proximity relationship toanother.

Addamiano, U.S. Pat. No. 4,556,436 (“Addamiano '436”) discusses aLely-type furnace system for forming thin films of beta silicon carbideon alpha silicon carbide which is characterized by a rapid cooling fromsublimation temperatures of between 2300° C. and 2700° C. to anothertemperature of less than 1800° C. Addamiano '436 notes that large singlecrystals of cubic (beta) silicon carbide are simply not available andthat growth of silicon carbide or other materials such as silicon ordiamond is rather difficult.

Hsu, U.S. Pat. No. 4,664,944, discusses a fluidized bed technique forforming silicon carbide crystals which resembles a chemical vapordeposition technique in its use of non-silicon carbide reactants, butwhich includes silicon carbide particles in the fluidized bed, thussomewhat resembling the sublimation technique.

German (Federal Republic) Patent No. 3,230,727 to Siemens Corporationdiscusses a silicon carbide sublimation technique in which the emphasisof the discussion is the minimization of the thermal gradient between asilicon carbide seed crystal and silicon carbide source material. Thispatent suggests limiting the thermal gradient to no more than 20° C. percentimeter of distance between source and seed in the reaction vessel.This patent also suggests that the overall vapor pressure in thesublimation system be kept in the range of between 1 and 5 millibar andpreferably around 1.5 to 2.5 millibar.

Davis, U.S. Pat. No. Re. 34,861 (“Davis '861”) discuss a method offorming large device quality single crystals of silicon carbide. Thispatent presents a sublimation process enhanced by maintaining a constantpolytype composition and size distribution in the source materials.These patents also discuss specific preparation of the growth surfaceand seed crystals and controlling the thermal gradient between thesource materials and the seed crystal.

Barrett, U.S. Pat. No. 5,746,827 (“Barrett '827”) discusses a method forproducing large diameter silicon carbide crystals requiring two growthstages. The first growth stage is to isothermally grow a seed crystal toa larger diameter. The second growth stage is to grow a large diameterboule from the seed crystal under thermal gradient conditions.

Hopkins, U.S. Pat. No. 5,873,937 (“Hopkins '937”) discusses a method forgrowing 4H silicon carbide crystals. This patent teaches a physicalvapor transport (PVT) system where the surface temperature of thecrystal is maintained at less than about 2160° C. and the pressureinside the PVT system is decreased to compensate for the lower growthtemperature.

Kitoh, U.S. Pat. No. 5,895,526 (“Kitoh '526”) teaches a sublimationprocess for growing a single silicon carbide crystal where the sublimedsource material flows parallel with the surface of a single crystalsubstrate.

Although significant progress in the production of SiC crystals hasoccurred over the years, commercially significant goals still remain forSiC crystal production. For example, faster and more powerful prototypedevices are being developed that require larger SiC crystals thatmaintain or improve upon current crystal quality. Boules large enough toproduce 50-mm diameter SiC wafers are currently at the far end ofcommercially viable SiC production. 75-mm diameter wafers of goodquality have been demonstrated but are not yet commercially availableand there is already a need for 100-mm wafers. Many SiC crystalproduction techniques are simply incapable of economically andconsistently producing crystals of the size and quality needed. Theprimary reason for the inability of most crystal production techniquesto keep up with commercial demand lies within the chemistry of SiC.

The chemistry of silicon carbide sublimation and crystallization is suchthat the known methods of growing silicon carbide crystals aredifficult, even when carried out successfully. The stoichiometry of thecrystal growth process is critical and complicated. Too much or toolittle silicon or carbon in the sublimed vapor may result in a crystalhaving an undesired polytype or imperfections such as micropipes.

Likewise, the high operating temperatures, typically above 2100° C. andthe necessity of forming specific temperature gradients within thecrystal growth system pose significant operational difficulties. Thetraditional graphite sublimation containers utilized in most sublimationsystems possess infrared emissivities on the order of 0.85 to 0.95depending upon the container's surface characteristics. Seed crystalsare heat sensitive to infrared radiation. Therefore, the infraredradiation emitted by the graphite containers can overheat the seedcrystal thereby complicating the precise temperature gradients necessaryfor successful operation of sublimation systems.

Recently, the SiC group at Linköping University presented a techniquefor the growth of SiC called High Temperature Chemical Vapor Deposition(“HTCVD”). O. Kordina, et al., “High Temperature Chemical VaporDeposition,” paper presented at the International Conference on SiC andRelated Materials, Kyoto, Japan, 1995; See also O. Kordina, et al., 69Applied Physics Letters, 1456 (1996). In this technique, the solidsilicon source material is replaced by gases such as silane. The use ofgaseous source materials improves control of the reaction stoichiometry.The solid carbon source material may also be replaced by a gas such aspropane; however, most of the carbon utilized in this technique actuallycomes from the graphite walls of the crucible. Theoretically, thistechnique's utilization of a continuous supply of gas would allowcontinuous and extended SiC boule growth. Unfortunately, the HTCVDtechnique has not proven commercially useful for boule growth primarilybecause the reaction destroys the graphite crucibles used in theprocess. Furthermore, the addition of hydrocarbon gases in thisparticular process tends to produce Si droplets encrusted with SiC whichdecreases efficiency and also ties up Si and C thereby altering thestoichiometry of the system.

Perhaps the most difficult aspect of silicon carbide growth is thereactivity of silicon at high temperatures. Silicon reacts with thegraphite containers utilized in most sublimation processes and, as notedabove, is encouraged to do so in some applications. This reaction isdifficult to control and usually results in too much silicon or too muchcarbon being present in the system thus undesirably altering thestoichiometry of the crystal growth process. In addition, silicon'sattack on the graphite container pits the walls of the containerdestroying the container and forming carbon dust which contaminates thecrystal.

In attempts to resolve these problems, some research has evaluated thatthe presence of tantalum in a sublimation system, e.g., Yu. A. Vodakovet al, “The Use of Tantalum Container Material for Quality Improvementof SiC Crystals Grown by the Sublimation Technique,” presented at the6^(th) International Conference on Silicon Carbide, September 1995,Kyoto, Japan. Some researchers opine that the presence of tantalum helpsmaintain the required stoichiometry for optimal crystal growth. Such anopinion is supported by reports that sublimation containers comprisingtantalum are less susceptible to attack by reactive silicon.

In a related application, WO97/27350 (“Vodakov '350”) Vodakov presents asublimation technique similar to that presented in U.S. Pat. No.4,147,572 and attempts to address the problem of silicon attacking thestructural components of the sublimation system. Vodakov '350 describesa geometry oriented sublimation technique in which solid silicon carbidesource materials and seed crystals are arranged in parallel closeproximity relationship to another. Vodakov '350 utilizes a sublimationcontainer made of solid tantalum. The inner surface of Vodakov'stantalum container is described as being an alloy of tantalum, siliconand carbon. Page 11, line 26 through page 12, line 10. Vodakov claimsthat such a container is resistive to attack by silicon vapor andcontributes to well-formed silicon carbide crystals.

The cost of tantalum is, however, a drawback to a sublimation processutilizing the container described in Vodakov. A sublimation container ofsolid tantalum is extremely expensive and like all sublimationcontainers, will eventually fail, making its long-term use uneconomic. Asolid tantalum sublimation container is also difficult to machine.Physically forming such a container is not an easy task. Lastly, thesublimation process of Vodakov '350 suffers the same deficiency shown inother solid source sublimation techniques in that it is not efficient atforming the large, high quality boules needed for newly discoveredapplications.

Therefore, a need exists for a process that provides for controlled,extended and repeatable growth of high quality SiC crystals. Such asystem must necessarily provide a container that is resistive to attackby silicon. Such a system should also be economical to implement anduse.

The GFS system of FIG. 9 comprises a crucible broadly designated at 910.It is to be understood that the crucible 910 is a substantially enclosedstructure similar to the type normally used in SiC sublimationtechniques. Reference is made to the crucible in Barrett '827; thegrowth chamber of Hopkins '937; and the crucibles shown in the figuresof Davis '861 as being exemplary, but not limiting, of the crucibles,vessels, or containers of the present embodiment. These references alsodemonstrate that the broad parameters of sublimation growth arerelatively well understood in this art. Accordingly, these will not beaddressed in detail herein, other than to describe the features of thepresent embodiment. The crucible 910 is generally cylindrical in shapeand includes a cylindrical wall 911 having an outer surface 912 and aninner surface 913. The cylindrical wall 911 is made of graphite coatedwith material characterized by a melting point above the sublimationtemperature of SiC. The coating material is also characterized bychemical inertness with respect to silicon and hydrogen at thetemperatures in question. Metal carbides and particularly the carbidesof tantalum, hafnium, niobium, titanium, zirconium, tungsten andvanadium and mixtures thereof exhibit the desired characteristics of therequired coating. Metal nitrides, and particularly the nitrides oftantalum, hafnium, niobium, titanium, zirconium, tungsten and vanadiumand mixtures thereof also exhibit the desired characteristics of therequired coating. Furthermore, mixtures of metal carbides and metalnitrides such as those listed previously may be used as the coatingsubstance. For ease of discussion and reference, the remainder of thedetailed description will refer to metal carbides although it isunderstood that the concepts and principles discussed herein are equallyapplicable to metal nitride coatings.

In all instances described herein, it is to be understood that graphitecomponents exposed to the source materials are coated with a metalcarbide coating. The metal carbide coating may be provided by any ofseveral commercially available coating processes such at that practicedby Ultramet Corporation of Pacoima, Calif. or Advance CeramicsCorporation of Lakewood, Ohio. Additionally, the graphite componentsdescribed herein are made from a graphite which has approximately thesame coefficient of thermal expansion as the selected metal carbide.Such materials are commercially available. The relative similarities ofthermal coefficients of expansion are a particular requirement formaterials heated to the extremely high temperatures described herein. Inthis manner, the likelihood of the graphite or metal carbide coatingcracking during the crystal growth process is substantially reduced andthe lifetime of the crucible will generally be increased.

The cylindrical wall 911 radially encloses a reaction area generallydesignated at 914. Outer 916 and inner 918 concentric source gaspathways supply the source gas materials to the reaction area 914.Although the source gases could be mixed prior to entering the reactionarea 914, separation of the source gases until each gas is heated toapproximately the reaction temperature helps prevent any undesired sidereactions between the silicon source gas and the carbon source gas. Theconcentric source gas pathways keep the source gas materials separatedfrom one another until the point where the source gases enter thereaction area 914. In a preferred embodiment the outer concentric sourcegas pathway 916 supplies the carbon source gas to the reaction area 914and the inner concentric source gas pathway 918 supplies the siliconsource gas.

In typical sublimation systems the graphite walls of the crucible areused as a source of carbon. The metal carbide coating diminishes theavailability of this source of carbon although it appears that undercertain circumstances the coated graphite may still act as a source ofsome carbon for the system. Accordingly, the majority of the carbonneeded is supplied from an outside source, such as a carbon source gas.Suitable carbon source gases include any hydrocarbon capable of reactingwith Si to form SiC: C₂ to C₈ hydrocarbons and in particular ethylene(C₂H₄) work. The carbon source gas stream may also comprise one or morecarrier gases such as He or H₂.

Suitable silicon source gases include any gas which will react withavailable carbon to form SiC. Silane (SiH₄) is probably the mostwell-known of the possible silicon source gases and works. Othersuitable sources of silicon include chlorosilane (SiH₄-xClx) andmethyltrichlorosilane (CH₃SiCl₃). Chlorosilanes require H₂ to react,however. The silicon source gas stream may also comprise a suitablyinert carrier gas such as He.

A seed crystal 922 is secured on a seed holder 920 and lowered into thereaction area 914. The source gases react within the reaction area 914to form SiC vapor which eventually deposits on the surface of the seedcrystal 922 to form a boule 924. It is believed that at least a portionof the SiC first deposits on the inner wall 913, then sublimes torecondense on the growth surface (seed crystal 922 or boule 924). Undermost circumstances, the seed crystal is preferably SiC of the samepolytype as the desired growth.

The composition of the source gases may be kept constant or variedduring the growth process depending upon the required stoichiometry,type of crystal desired and the physical characteristics of the crystalgrowth system.

Those familiar with the physical chemistry of solids, liquids and gasesknow that crystal growth is in most circumstances encouraged on a growthsurface if the surface is at a somewhat lower temperature than the fluid(either gas or liquid) which carries the molecules or atoms to becondensed. The GFS system is no exception. A thermal gradient isestablished between the growth surface and the source material. Althoughthe exact dimensions of the temperature gradient may vary depending uponthe pressure of the system, desired polytype, source gas composition,etc., the following general principle is usually applicable to all typesof SiC crystal growth processes, including the GFS system. Thetemperature of the silicon source and carbon source should be raised toa temperature sufficient for the formation of the vaporized specieswhile the temperature of the crystal growth surface is elevated to atemperature approaching the temperature of silicon and carbon sources,but lower than the temperature of the silicon and carbon sources, andlower than that at which SiC will sublime faster than deposit under thegas pressure conditions utilized.

As stated above, numerous variables determine the appropriatetemperature gradient for a given system. However, a system such as thatdescribed in FIG. 1 is discovered to operate well at seed temperaturesbetween about 1900° C. and about 2500° C. with the inner walls of thereaction area being about 150° C. to about 200° C. hotter than the seed.The maximum growth rate for such a system has yet to be determined.Higher temperatures are known to generally translate into faster growthrates. Higher temperatures, however, can result in sublimation of theseed, which alters the equilibrium of the system and requires additionalsource gas and potentially other adjustments as well.

The GFS system of FIG. 1 has demonstrated the ability to produce verylarge high quality crystals of SiC. More importantly, the GFS system ofFIG. 1 has demonstrated an ability to withstand attack from the Sicompounds that eventually destroy typical graphite crucibles. A testcrucible of graphite coated with an approximately 30 micron thickcoating of TaC emerged from a crystal growth session unaffected by theharsh environment. Only after several runs have cracks appeared in testcrucibles, usually near a sharp corner where the metal carbide coatingwas less than optimum. However, even when the coating cracks, thecrystal growth system is not subject to the carbon dust typically formedwhen a graphite crucible's integrity is compromised.

The explanation for this surprising property is not fully understood.Although the inventors do not wish to be bound by any particular theory,one possible explanation is that when uncoated graphite is attacked bySi, the Si predominately attacks the weak parts of the graphite, i.e.,at the grain boundaries penetrating into the pores. The Si forms SiCwhich sublimes and is removed as a volatile species. Eventually Sicompletely erodes the graphite surrounding the grain, leaving the grainbehind as a carbon dust particle. It is believed that the metal carbidecoating penetrates deep within the graphite pores causing the Si toattack the graphite in a more uniform manner, thereby avoiding thegeneration of carbon dust.

Surprisingly, a graphite crucible once coated with a metal carbideresists the formation of carbon dust even after substantial spalling ofthe metal carbide coating. Accordingly, an alternative embodiment is aGFS system comprising a graphite crucible which has at one time beencoated with a metal carbide coating but which through use or othercircumstances has lost some or all of its metal carbide coating. Such asystem is capable is producing quality SiC crystals withoutcontamination from carbon dust.

Additionally, the GFS system of FIG. 1 has demonstrated the ability toprovide improved control of the temperature gradients within the crystalgrowth system. As discussed previously, seed crystals are sensitive toinfrared radiation and graphite possesses an infrared emissivity ofbetween about 0.85 to about 0.95 depending upon the surface of thegraphite. In contrast the infrared emissivity of the metal compoundcoatings of the embodiment range from approximately 0.4 for ZrC toapproximately 0.5 for TaC to approximately 0.6 for NbC. The loweremissivities of the metal compound coatings of the embodimentsubstantially reduce the amount of infrared radiation impinging upon theseed crystal during crystal growth and can result in a 100° C. or morereduction in seed temperature when compared to uncoated graphitesystems. Reducing the amount of infrared radiation removes a potentialsource of excess heat from the system thereby improving control of thetemperature gradients within the system.

It is readily apparent to one skilled in the art that the utilization ofa metal carbide coated crucible as described above is readily adaptableto existing SiC crystal growth systems. It will be additionally apparentto those familiar with this art that the use of metal carbide-coatedcrucibles according to the present embodiment need not be limited to thesublimation growth of SiC. Thus, although the embodiment offersparticular advantages with respect to SiC growth, the coatings andcoated crucibles, vessels or containers described herein offerstructural and functional advantages for the growth of other materials,including other wide band-gap semiconductor materials such as the GroupI IInitrides, and particularly including gallium nitride (GaN). Forexample, some researchers have reported a link between the presence ofcarbon and a yellow luminescence in GaN and non-uniform electricalbehavior in In-containing nitrides. Pearton et al, GaN: Processing,Defects and Devices, 86 Applied Physics Reviews, 1 (July 1999). Theutilization of the coated apparatus and method of the embodimentadvantageously reduces the availability of carbon as a potentialresidual impurity in MOCVD nitrides.

FIG. 10 illustrates a cross-sectional view of another GFS system used inaccordance with the method of the present embodiment. The crucible isbroadly designated at 1010. The crucible 1010 is located within afurnace indicated generally at 108. Methods and apparatus, such as afurnace, for supplying heat to SiC and other crystal growth systems arewell known to those skilled in the art, and thus will not be otherwisediscussed in detail herein.

The crucible 1010 is generally cylindrical in shape and includes a lid1026 and a bottom 1028 that substantially encloses an intermediatecylindrical portion 1030. The intermediate cylindrical portion 1030comprises an outer cylinder 1032 having a top and a bottom and an innerdiameter and an outer diameter. Situated within the inner diameter ofthe outer cylinder 1032 is an inner cylinder 1034 also having a top anda bottom, and an inner diameter and an outer diameter. The outercylinder 1032 and the inner cylinder 1034 form inner 1038 and outer 1036concentric gas pathways.

In a preferred embodiment the intermediate cylindrical portion 1030 alsocomprises at least one spacer ring 1040 situated between the outercylinder 1032 and the lid 1026. The spacer ring 1040 is defined by aninner diameter and an outer diameter with said inner diameter being lessthan the outer diameter of the inner cylinder 1034. The spacer ring 1040and the lid 1026 generally define a reaction area 1042 above the outerand inner cylinders 1032 and 1034 respectively. It is to be understoodthat the spacer ring 40 is an optional component. When used, however,the spacer ring 1040 preferably incorporates the refractory metalcarbide coating of the present embodiment. Alternatively, the outercylinder 1032 can be extended to replace the spacer ring 1040. However,the use of a spacer ring or rings is recommended because of theflexibility provided in adjusting the size of the reaction area 1042 andthus the thermal gradient. In a further alternative, the spacer ring1040 can be used in conjunction with other similarly shaped devices suchas a growth disk (a ring with a venturi-like opening that focuses upwardflowing SiC vapor) or a collection disk (a porous disk that allows SiCvapor to flow upward while collecting solid particles that fall from thewalls of the crucible). Collecting these particles onto a hot collectiondisk permits them to resublime and contribute to the growth of thecrystal.

Extending into the reaction area 1042 from the lid 1026 is a seedcrystal 1044 supported by a seed holder 1046 and a graphite rod 1048.The seed crystal 1044 acts as a substrate for the growth of a SiC boule1050.

Two gas sources 1052 and 1054 are in fluid communication with the innerand outer concentric gas pathways and provide the silicon and carbonsource gases utilized in the SiC crystal growth process. In a preferredembodiment one gas source 1052 supplies the carbon source gas to theouter concentric gas pathway 1036 and the other gas source 1054 suppliesthe silicon source gas to the inner concentric gas pathway 1038. Thereaction to form SiC vapor and the desired SiC boule proceeds aspreviously described with respect to FIG. 9 . A gas outlet 1027incorporated into the lid 1026 and extending through the underlying seedholder 1046 provides a means for evacuation of gas from the reactionarea 1042.

It will be further understood that relevant portions of the systemsreferred to earlier (e.g., Davis, Vodakov, etc.) could be modified andimproved to incorporate the coated surfaces, vessels, and systemsdescribed herein, and would thus fall within the parameters of thepresent embodiment.

Example 29

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 7,501,022 the entiredisclosure of which is incorporated herein by reference.

Example 30

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 8,377,806 the entiredisclosure of which is incorporated herein by reference.

Example 31

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 6,706,114 the entiredisclosure of which is incorporated herein by reference.

Example 32

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 8,492,827 the entiredisclosure of which is incorporated herein by reference.

Example 33

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 8,329,133 the entiredisclosure of which is incorporated herein by reference.

Example 33

6-nine pure, and preferably 7-nines pure (greater purity may also beused) polysilocarb derived SiC or SiOC that is disclosed and taught inpatent applications, Ser. No. 14/864,539 (US Publication No.2016/0208412), Ser. No. 14/864,125 (US Publication No. 2016/0207782),and PCT/US2015/051997 (Publication No. WO 2016/049344) is used, forexample as, seed crystals, starting crystal, growth material, sourcematerial, deposition material or raw material, is used in the apparatusand processes taught and disclosed in U.S. Pat. No. 60,191,841 theentire disclosure of which is incorporated herein by reference.

It is noted that there is no requirement to provide or address thetheory underlying the novel and groundbreaking processes, materials,performance or other beneficial features and properties that are thesubject of, or associated with, embodiments of the present inventions.Nevertheless, various theories are provided in this specification tofurther advance the art in this area. These theories put forth in thisspecification, and unless expressly stated otherwise, in no way limit,restrict or narrow the scope of protection to be afforded the claimedinventions. These theories many not be required or practiced to utilizethe present inventions. It is further understood that the presentinventions may lead to new, and heretofore unknown theories to explainthe function-features of embodiments of the methods, articles,materials, devices and system of the present inventions; and such laterdeveloped theories shall not limit the scope of protection afforded thepresent inventions.

The various embodiments of formulations, batches, materials,compositions, devices, systems, apparatus, operations activities andmethods set forth in this specification may be used in the variousfields where SiC and Si find applicability, as well as, in other fields,where SiC, Si and both, have been unable to perform in a viable manner(either cost, performance or both). Additionally, these variousembodiments set forth in this specification may be used with each otherin different and various combinations. Thus, for example, theconfigurations provided in the various embodiments of this specificationmay be used with each other; and the scope of protection afforded thepresent inventions should not be limited to a particular embodiment,configuration or arrangement that is set forth in a particularembodiment, example, or in an embodiment in a particular Figure.

The inventions may be embodied in other forms than those specificallydisclosed herein without departing from their spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive.

What is claimed:
 1. A method of making boule for the production of a 4HN-Type silicon carbide wafer, having a diameter of from about 6 inchesto about 10 inches, the wafer characterized with properties comprising:type/dopant:N/nitrogen; orientation:<0001>4.0°±0.5°; thickness: about300 to about 800 μm; and, micropipe density of <1 cm⁻²; and, the methodcomprising the steps of: forming a vapor of a polymer derived ceramicSiC starting material, wherein the polymer derived ceramic SiC startingmaterial has a purity of at least about 6 nines, and is oxide layerfree; depositing the vapor on a seed crystal to form a boule; andproviding the boule to a wafer manufacturing process.
 2. The method ofclaim 1, wherein the wafer is further characterized with a propertycomprising RT 0.02-0.2 Ω·cm.
 3. The method of claim 2 wherein the wafermanufacturing process produces a wafer having improved features, whencompared to a wafer made from a non-polymer derived SiC material.
 4. Themethod of claim 1, wherein the wafer is further characterized with aproperty comprising RT 0.01-0.1 Ω·cm.
 5. The method of claim 4 whereinthe wafer manufacturing process produces a wafer having improvedfeatures, when compared to a wafer made from a non-polymer derived SiCmaterial.
 6. The method of claim 1, wherein the wafer is furthercharacterized with a property comprising RT: 0.1-40 Ω·cm.
 7. The methodof claim 6 wherein the wafer manufacturing process produces a waferhaving improved features, when compared to a wafer made from anon-polymer derived SiC material.
 8. The methods of claim 1, 2, 4 or 6,wherein the seed crystal comprises a polymer derived ceramic SiC.
 9. Themethod of claim 1 wherein the wafer manufacturing process produces awafer having improved features, when compared to a wafer made from anon-polymer derived SiC material.
 10. The methods of claim 9, 3, 5 or 7,wherein the improved features are selected from the group consisting ofbow, edge contour, flatness, focal plane, warp and site flatness.
 11. Amethod of making a 4H silicon carbide wafer, the method comprising thesteps of forming a vapor of a polymer derived ceramic SiC, the polymerderived ceramic having a purity of at least about 6 nines, and beingoxide layer free, depositing the vapor on a seed crystal to form aboule, and providing the boule to a wafer manufacturing process, whereinthe boule has a diameter of from about 6 inches to about 10 inches. 12.The method of claim 11, wherein the seed crystal comprises a polymerderived ceramic 4H SiC.
 13. The method of claim 11, wherein the wafermanufacturing process produces a wafer having improved features, whencompared to a wafer made from a non-polymer derived SiC material, theimproved features selected from the group consisting of bow, edgecontour, flatness, focal plane, warp and site flatness.
 14. A method ofmaking boule for the production of a 4H N-Type silicon carbide wafer,having a diameter of from about 4 inches to about 10 inches, the wafercharacterized with properties comprising: type/dopant:N/nitrogen;orientation:<0001>4.0°±0.5°; thickness: about 300 to about 800 μm; and,micropipe density of <1 cm⁻²; and, RT:0.01-40 Ω·cm; and, Bow/Warp/TTV<45μm; the method comprising the steps of: forming a vapor of a polymerderived ceramic SiC starting material; wherein the polymer derivedceramic SiC starting material has a purity of at least about 6 nines;depositing the vapor on a seed crystal to form a boule; and providingthe boule to a wafer manufacturing process.
 15. The method of claim 14,wherein the seed crystal is polymer derived ceramic SiC.
 16. The methodsof claim 14, wherein the RT is 0.1-40 Ω·cm.
 17. The methods of claim 14,wherein the RT is 0.02-0.2 Ω·cm.
 18. The methods of claim 14, 15, 16, or17, wherein the Bow/Warp/TTV is <35 μm.
 19. The methods of claim 14, 15,16, or 17, wherein the Bow/Warp/TTV is <25 μm.
 20. A method of makingboule for the production of a 4H N-Type silicon carbide wafer, having adiameter of from about 8 inches to about 12 inches, the wafercharacterized with properties comprising: type/dopant:N/nitrogen;orientation:<0001>4.0°±0.5°; thickness: about 300 to about 800 μm; and,micropipe density of <1 cm⁻²; and, the method comprising the steps of:forming a vapor of a polymer derived ceramic SiC starting material,wherein the polymer derived ceramic SiC starting material has a purityof at least about 6 nines, and is oxide layer free; depositing the vaporon a seed crystal to form a boule; and providing the boule to a wafermanufacturing process.
 21. A method of making a 4H silicon carbidewafer, the method comprising the steps of forming a vapor of a polymerderived ceramic SiC, the polymer derived ceramic having a purity of atleast about 6 nines, and being oxide layer free, depositing the vapor ona seed crystal to form a boule, and providing the boule to a wafermanufacturing process, wherein the boule has a diameter of from about 8″to about 12″.
 22. A method of making boule for the production of a 4HN-Type silicon carbide wafer, having a diameter of from about 8 inchesto about 12 inches, the wafer characterized with properties comprising:type/dopant:N/nitrogen; orientation:<0001>4.0°±0.5°; thickness: about300 to about 800 μm; and, micropipe density of <1 cm⁻²; and, RT:0.01-40Ω·cm; and, Bow/Warp/TTV<45 μm; the method comprising the steps of:forming a vapor of a polymer derived ceramic SiC starting material;wherein the polymer derived ceramic SiC starting material has a purityof at least about 6 nines; depositing the vapor on a seed crystal toform a boule; and providing the boule to a wafer manufacturing process.